(mkosarek) Beginning to explain rigidbody physics in a reasonable way

5 files changed, 235 insertions, 121 deletions

diff --git a/2d/rigidbody/rigidbody_1/dist/output.js b/2d/rigidbody/rigidbody_1/dist/output.js
index 9ba383a..9fdc721 100644
--- a/2d/rigidbody/rigidbody_1/dist/output.js
+++ b/2d/rigidbody/rigidbody_1/dist/output.js
@@ -609,7 +609,7 @@ if (typeof WebAssembly !== 'object') {
 function setValue(ptr, value, type, noSafe) {
   type = type || 'i8';
   if (type.charAt(type.length-1) === '*') type = 'i32'; // pointers are 32-bit
-    switch(type) {
+    switch (type) {
       case 'i1': HEAP8[((ptr)>>0)] = value; break;
       case 'i8': HEAP8[((ptr)>>0)] = value; break;
       case 'i16': HEAP16[((ptr)>>1)] = value; break;
@@ -627,7 +627,7 @@ function setValue(ptr, value, type, noSafe) {
 function getValue(ptr, type, noSafe) {
   type = type || 'i8';
   if (type.charAt(type.length-1) === '*') type = 'i32'; // pointers are 32-bit
-    switch(type) {
+    switch (type) {
       case 'i1': return HEAP8[((ptr)>>0)];
       case 'i8': return HEAP8[((ptr)>>0)];
       case 'i16': return HEAP16[((ptr)>>1)];
@@ -808,7 +808,7 @@ function UTF8ArrayToString(heap, idx, maxBytesToRead) {
       if ((u0 & 0xF0) == 0xE0) {
         u0 = ((u0 & 15) << 12) | (u1 << 6) | u2;
       } else {
-        if ((u0 & 0xF8) != 0xF0) warnOnce('Invalid UTF-8 leading byte 0x' + u0.toString(16) + ' encountered when deserializing a UTF-8 string on the asm.js/wasm heap to a JS string!');
+        if ((u0 & 0xF8) != 0xF0) warnOnce('Invalid UTF-8 leading byte 0x' + u0.toString(16) + ' encountered when deserializing a UTF-8 string in wasm memory to a JS string!');
         u0 = ((u0 & 7) << 18) | (u1 << 12) | (u2 << 6) | (heap[idx++] & 63);
       }
 
@@ -884,7 +884,7 @@ function stringToUTF8Array(str, heap, outIdx, maxBytesToWrite) {
       heap[outIdx++] = 0x80 | (u & 63);
     } else {
       if (outIdx + 3 >= endIdx) break;
-      if (u >= 0x200000) warnOnce('Invalid Unicode code point 0x' + u.toString(16) + ' encountered when serializing a JS string to an UTF-8 string on the asm.js/wasm heap! (Valid unicode code points should be in range 0-0x1FFFFF).');
+      if (u >= 0x200000) warnOnce('Invalid Unicode code point 0x' + u.toString(16) + ' encountered when serializing a JS string to a UTF-8 string in wasm memory! (Valid unicode code points should be in range 0-0x1FFFFF).');
       heap[outIdx++] = 0xF0 | (u >> 18);
       heap[outIdx++] = 0x80 | ((u >> 12) & 63);
       heap[outIdx++] = 0x80 | ((u >> 6) & 63);
@@ -1252,12 +1252,12 @@ function checkStackCookie() {
 // include: runtime_assertions.js
 
 
-// Endianness check (note: assumes compiler arch was little-endian)
+// Endianness check
 (function() {
   var h16 = new Int16Array(1);
   var h8 = new Int8Array(h16.buffer);
   h16[0] = 0x6373;
-  if (h8[0] !== 0x73 || h8[1] !== 0x63) throw 'Runtime error: expected the system to be little-endian!';
+  if (h8[0] !== 0x73 || h8[1] !== 0x63) throw 'Runtime error: expected the system to be little-endian! (Run with -s SUPPORT_BIG_ENDIAN=1 to bypass)';
 })();
 
 function abortFnPtrError(ptr, sig) {
@@ -1274,8 +1274,6 @@ var __ATPOSTRUN__ = []; // functions called after the main() is called
 var runtimeInitialized = false;
 var runtimeExited = false;
 
-__ATINIT__.push({ func: function() { ___wasm_call_ctors() } });
-
 function preRun() {
 
   if (Module['preRun']) {
@@ -1292,6 +1290,7 @@ function initRuntime() {
   checkStackCookie();
   assert(!runtimeInitialized);
   runtimeInitialized = true;
+
   
   callRuntimeCallbacks(__ATINIT__);
 }
@@ -1616,6 +1615,8 @@ function createWasm() {
     wasmTable = Module['asm']['__indirect_function_table'];
     assert(wasmTable, "table not found in wasm exports");
 
+    addOnInit(Module['asm']['__wasm_call_ctors']);
+
     removeRunDependency('wasm-instantiate');
   }
   // we can't run yet (except in a pthread, where we have a custom sync instantiator)
@@ -1637,7 +1638,8 @@ function createWasm() {
 
   function instantiateArrayBuffer(receiver) {
     return getBinaryPromise().then(function(binary) {
-      return WebAssembly.instantiate(binary, info);
+      var result = WebAssembly.instantiate(binary, info);
+      return result;
     }).then(receiver, function(reason) {
       err('failed to asynchronously prepare wasm: ' + reason);
 
@@ -1704,12 +1706,8 @@ var ASM_CONSTS = {
 
 
 
-  function abortStackOverflow(allocSize) {
-      abort('Stack overflow! Attempted to allocate ' + allocSize + ' bytes on the stack, but stack has only ' + (_emscripten_stack_get_free() + allocSize) + ' bytes available!');
-    }
-
   function callRuntimeCallbacks(callbacks) {
-      while(callbacks.length > 0) {
+      while (callbacks.length > 0) {
         var callback = callbacks.shift();
         if (typeof callback == 'function') {
           callback(Module); // Pass the module as the first argument.
@@ -1760,6 +1758,11 @@ var ASM_CONSTS = {
       return error.stack.toString();
     }
 
+  var runtimeKeepaliveCounter=0;
+  function keepRuntimeAlive() {
+      return noExitRuntime || runtimeKeepaliveCounter > 0;
+    }
+
   function stackTrace() {
       var js = jsStackTrace();
       if (Module['extraStackTrace']) js += '\n' + Module['extraStackTrace']();
@@ -1783,10 +1786,6 @@ var ASM_CONSTS = {
       return requestAnimationFrame(tick);
     }
 
-  function _emscripten_get_heap_size() {
-      return HEAPU8.length;
-    }
-  
   function emscripten_realloc_buffer(size) {
       try {
         // round size grow request up to wasm page size (fixed 64KB per spec)
@@ -1800,7 +1799,8 @@ var ASM_CONSTS = {
       // anyhow)
     }
   function _emscripten_resize_heap(requestedSize) {
-      var oldSize = _emscripten_get_heap_size();
+      var oldSize = HEAPU8.length;
+      requestedSize = requestedSize >>> 0;
       // With pthreads, races can happen (another thread might increase the size in between), so return a failure, and let the caller retry.
       assert(requestedSize > oldSize);
   
@@ -1827,7 +1827,7 @@ var ASM_CONSTS = {
   
       // Loop through potential heap size increases. If we attempt a too eager reservation that fails, cut down on the
       // attempted size and reserve a smaller bump instead. (max 3 times, chosen somewhat arbitrarily)
-      for(var cutDown = 1; cutDown <= 4; cutDown *= 2) {
+      for (var cutDown = 1; cutDown <= 4; cutDown *= 2) {
         var overGrownHeapSize = oldSize * (1 + 0.2 / cutDown); // ensure geometric growth
         // but limit overreserving (default to capping at +96MB overgrowth at most)
         overGrownHeapSize = Math.min(overGrownHeapSize, requestedSize + 100663296 );
@@ -1845,7 +1845,7 @@ var ASM_CONSTS = {
     }
 
   var JSEvents={inEventHandler:0,removeAllEventListeners:function() {
-        for(var i = JSEvents.eventHandlers.length-1; i >= 0; --i) {
+        for (var i = JSEvents.eventHandlers.length-1; i >= 0; --i) {
           JSEvents._removeHandler(i);
         }
         JSEvents.eventHandlers = [];
@@ -1859,13 +1859,13 @@ var ASM_CONSTS = {
         function arraysHaveEqualContent(arrA, arrB) {
           if (arrA.length != arrB.length) return false;
   
-          for(var i in arrA) {
+          for (var i in arrA) {
             if (arrA[i] != arrB[i]) return false;
           }
           return true;
         }
         // Test if the given call was already queued, and if so, don't add it again.
-        for(var i in JSEvents.deferredCalls) {
+        for (var i in JSEvents.deferredCalls) {
           var call = JSEvents.deferredCalls[i];
           if (call.targetFunction == targetFunction && arraysHaveEqualContent(call.argsList, argsList)) {
             return;
@@ -1879,7 +1879,7 @@ var ASM_CONSTS = {
   
         JSEvents.deferredCalls.sort(function(x,y) { return x.precedence < y.precedence; });
       },removeDeferredCalls:function(targetFunction) {
-        for(var i = 0; i < JSEvents.deferredCalls.length; ++i) {
+        for (var i = 0; i < JSEvents.deferredCalls.length; ++i) {
           if (JSEvents.deferredCalls[i].targetFunction == targetFunction) {
             JSEvents.deferredCalls.splice(i, 1);
             --i;
@@ -1891,14 +1891,14 @@ var ASM_CONSTS = {
         if (!JSEvents.canPerformEventHandlerRequests()) {
           return;
         }
-        for(var i = 0; i < JSEvents.deferredCalls.length; ++i) {
+        for (var i = 0; i < JSEvents.deferredCalls.length; ++i) {
           var call = JSEvents.deferredCalls[i];
           JSEvents.deferredCalls.splice(i, 1);
           --i;
           call.targetFunction.apply(null, call.argsList);
         }
       },eventHandlers:[],removeAllHandlersOnTarget:function(target, eventTypeString) {
-        for(var i = 0; i < JSEvents.eventHandlers.length; ++i) {
+        for (var i = 0; i < JSEvents.eventHandlers.length; ++i) {
           if (JSEvents.eventHandlers[i].target == target && 
             (!eventTypeString || eventTypeString == JSEvents.eventHandlers[i].eventTypeString)) {
              JSEvents._removeHandler(i--);
@@ -1929,7 +1929,7 @@ var ASM_CONSTS = {
           JSEvents.eventHandlers.push(eventHandler);
           JSEvents.registerRemoveEventListeners();
         } else {
-          for(var i = 0; i < JSEvents.eventHandlers.length; ++i) {
+          for (var i = 0; i < JSEvents.eventHandlers.length; ++i) {
             if (JSEvents.eventHandlers[i].target == eventHandler.target
              && JSEvents.eventHandlers[i].eventTypeString == eventHandler.eventTypeString) {
                JSEvents._removeHandler(i--);
@@ -2079,7 +2079,7 @@ var ASM_CONSTS = {
       // Closure is expected to be allowed to minify the '.multiDrawWebgl' property, so not accessing it quoted.
       return !!(ctx.multiDrawWebgl = ctx.getExtension('WEBGL_multi_draw'));
     }
-  var GL={counter:1,buffers:[],mappedBuffers:{},programs:[],framebuffers:[],renderbuffers:[],textures:[],uniforms:[],shaders:[],vaos:[],contexts:[],offscreenCanvases:{},timerQueriesEXT:[],queries:[],samplers:[],transformFeedbacks:[],syncs:[],byteSizeByTypeRoot:5120,byteSizeByType:[1,1,2,2,4,4,4,2,3,4,8],programInfos:{},stringCache:{},stringiCache:{},unpackAlignment:4,recordError:function recordError(errorCode) {
+  var GL={counter:1,buffers:[],mappedBuffers:{},programs:[],framebuffers:[],renderbuffers:[],textures:[],shaders:[],vaos:[],contexts:[],offscreenCanvases:{},queries:[],samplers:[],transformFeedbacks:[],syncs:[],byteSizeByTypeRoot:5120,byteSizeByType:[1,1,2,2,4,4,4,2,3,4,8],stringCache:{},stringiCache:{},unpackAlignment:4,recordError:function recordError(errorCode) {
         if (!GL.lastError) {
           GL.lastError = errorCode;
         }
@@ -2090,7 +2090,7 @@ var ASM_CONSTS = {
         }
         return ret;
       },MAX_TEMP_BUFFER_SIZE:2097152,numTempVertexBuffersPerSize:64,log2ceilLookup:function(i) {
-        return 32 - Math.clz32(i-1);
+        return 32 - Math.clz32(i === 0 ? 0 : i - 1);
       },generateTempBuffers:function(quads, context) {
         var largestIndex = GL.log2ceilLookup(GL.MAX_TEMP_BUFFER_SIZE);
         context.tempVertexBufferCounters1 = [];
@@ -2218,6 +2218,19 @@ var ASM_CONSTS = {
         }
       },createContext:function(canvas, webGLContextAttributes) {
   
+        // BUG: Workaround Safari WebGL issue: After successfully acquiring WebGL context on a canvas,
+        // calling .getContext() will always return that context independent of which 'webgl' or 'webgl2'
+        // context version was passed. See https://bugs.webkit.org/show_bug.cgi?id=222758 and
+        // https://github.com/emscripten-core/emscripten/issues/13295.
+        // TODO: Once the bug is fixed and shipped in Safari, adjust the Safari version field in above check.
+        if (!canvas.getContextSafariWebGL2Fixed) {
+          canvas.getContextSafariWebGL2Fixed = canvas.getContext;
+          canvas.getContext = function(ver, attrs) {
+            var gl = canvas.getContextSafariWebGL2Fixed(ver, attrs);
+            return ((ver == 'webgl') == (gl instanceof WebGLRenderingContext)) ? gl : null;
+          }
+        }
+  
         var ctx = 
           (webGLContextAttributes.majorVersion > 1)
           ?
@@ -2290,7 +2303,21 @@ var ASM_CONSTS = {
         __webgl_enable_WEBGL_draw_instanced_base_vertex_base_instance(GLctx);
         __webgl_enable_WEBGL_multi_draw_instanced_base_vertex_base_instance(GLctx);
   
-        GLctx.disjointTimerQueryExt = GLctx.getExtension("EXT_disjoint_timer_query");
+        // On WebGL 2, EXT_disjoint_timer_query is replaced with an alternative
+        // that's based on core APIs, and exposes only the queryCounterEXT()
+        // entrypoint.
+        if (context.version >= 2) {
+          GLctx.disjointTimerQueryExt = GLctx.getExtension("EXT_disjoint_timer_query_webgl2");
+        }
+  
+        // However, Firefox exposes the WebGL 1 version on WebGL 2 as well and
+        // thus we look for the WebGL 1 version again if the WebGL 2 version
+        // isn't present. https://bugzilla.mozilla.org/show_bug.cgi?id=1328882
+        if (context.version < 2 || !GLctx.disjointTimerQueryExt)
+        {
+          GLctx.disjointTimerQueryExt = GLctx.getExtension("EXT_disjoint_timer_query");
+        }
+  
         __webgl_enable_WEBGL_multi_draw(GLctx);
   
         // .getSupportedExtensions() can return null if context is lost, so coerce to empty array.
@@ -2302,49 +2329,6 @@ var ASM_CONSTS = {
             GLctx.getExtension(ext);
           }
         });
-      },populateUniformTable:function(program) {
-        var p = GL.programs[program];
-        var ptable = GL.programInfos[program] = {
-          uniforms: {},
-          maxUniformLength: 0, // This is eagerly computed below, since we already enumerate all uniforms anyway.
-          maxAttributeLength: -1, // This is lazily computed and cached, computed when/if first asked, "-1" meaning not computed yet.
-          maxUniformBlockNameLength: -1 // Lazily computed as well
-        };
-  
-        var utable = ptable.uniforms;
-        // A program's uniform table maps the string name of an uniform to an integer location of that uniform.
-        // The global GL.uniforms map maps integer locations to WebGLUniformLocations.
-        var numUniforms = GLctx.getProgramParameter(p, 0x8B86/*GL_ACTIVE_UNIFORMS*/);
-        for (var i = 0; i < numUniforms; ++i) {
-          var u = GLctx.getActiveUniform(p, i);
-  
-          var name = u.name;
-          ptable.maxUniformLength = Math.max(ptable.maxUniformLength, name.length+1);
-  
-          // If we are dealing with an array, e.g. vec4 foo[3], strip off the array index part to canonicalize that "foo", "foo[]",
-          // and "foo[0]" will mean the same. Loop below will populate foo[1] and foo[2].
-          if (name.slice(-1) == ']') {
-            name = name.slice(0, name.lastIndexOf('['));
-          }
-  
-          // Optimize memory usage slightly: If we have an array of uniforms, e.g. 'vec3 colors[3];', then
-          // only store the string 'colors' in utable, and 'colors[0]', 'colors[1]' and 'colors[2]' will be parsed as 'colors'+i.
-          // Note that for the GL.uniforms table, we still need to fetch the all WebGLUniformLocations for all the indices.
-          var loc = GLctx.getUniformLocation(p, name);
-          if (loc) {
-            var id = GL.getNewId(GL.uniforms);
-            utable[name] = [u.size, id];
-            GL.uniforms[id] = loc;
-  
-            for (var j = 1; j < u.size; ++j) {
-              var n = name + '['+j+']';
-              loc = GLctx.getUniformLocation(p, n);
-              id = GL.getNewId(GL.uniforms);
-  
-              GL.uniforms[id] = loc;
-            }
-          }
-        }
       }};
   
   var __emscripten_webgl_power_preferences=['default', 'low-power', 'high-performance'];
@@ -2391,7 +2375,7 @@ var ASM_CONSTS = {
   function _emscripten_webgl_init_context_attributes(attributes) {
       assert(attributes);
       var a = attributes >> 2;
-      for(var i = 0; i < (56>>2); ++i) {
+      for (var i = 0; i < (56>>2); ++i) {
         HEAP32[a+i] = 0;
       }
   
@@ -2455,8 +2439,7 @@ var ASM_CONSTS = {
     }
 
   function _glAttachShader(program, shader) {
-      GLctx.attachShader(GL.programs[program],
-                              GL.shaders[shader]);
+      GLctx.attachShader(GL.programs[program], GL.shaders[shader]);
     }
 
   function _glBindBuffer(target, buffer) {
@@ -2516,7 +2499,11 @@ var ASM_CONSTS = {
   function _glCreateProgram() {
       var id = GL.getNewId(GL.programs);
       var program = GLctx.createProgram();
+      // Store additional information needed for each shader program:
       program.name = id;
+      // Lazy cache results of glGetProgramiv(GL_ACTIVE_UNIFORM_MAX_LENGTH/GL_ACTIVE_ATTRIBUTE_MAX_LENGTH/GL_ACTIVE_UNIFORM_BLOCK_MAX_NAME_LENGTH)
+      program.maxUniformLength = program.maxAttributeLength = program.maxUniformBlockNameLength = 0;
+      program.uniformIdCounter = 1;
       GL.programs[id] = program;
       return id;
     }
@@ -2524,6 +2511,7 @@ var ASM_CONSTS = {
   function _glCreateShader(shaderType) {
       var id = GL.getNewId(GL.shaders);
       GL.shaders[id] = GLctx.createShader(shaderType);
+  
       return id;
     }
 
@@ -2557,7 +2545,6 @@ var ASM_CONSTS = {
       GLctx.deleteProgram(program);
       program.name = 0;
       GL.programs[id] = null;
-      GL.programInfos[id] = null;
     }
 
   function _glDeleteShader(id) {
@@ -2650,42 +2637,35 @@ var ASM_CONSTS = {
         return;
       }
   
-      var ptable = GL.programInfos[program];
-      if (!ptable) {
-        GL.recordError(0x502 /* GL_INVALID_OPERATION */);
-        return;
-      }
+      program = GL.programs[program];
   
       if (pname == 0x8B84) { // GL_INFO_LOG_LENGTH
-        var log = GLctx.getProgramInfoLog(GL.programs[program]);
+        var log = GLctx.getProgramInfoLog(program);
         if (log === null) log = '(unknown error)';
         HEAP32[((p)>>2)] = log.length + 1;
       } else if (pname == 0x8B87 /* GL_ACTIVE_UNIFORM_MAX_LENGTH */) {
-        HEAP32[((p)>>2)] = ptable.maxUniformLength;
+        if (!program.maxUniformLength) {
+          for (var i = 0; i < GLctx.getProgramParameter(program, 0x8B86/*GL_ACTIVE_UNIFORMS*/); ++i) {
+            program.maxUniformLength = Math.max(program.maxUniformLength, GLctx.getActiveUniform(program, i).name.length+1);
+          }
+        }
+        HEAP32[((p)>>2)] = program.maxUniformLength;
       } else if (pname == 0x8B8A /* GL_ACTIVE_ATTRIBUTE_MAX_LENGTH */) {
-        if (ptable.maxAttributeLength == -1) {
-          program = GL.programs[program];
-          var numAttribs = GLctx.getProgramParameter(program, 0x8B89/*GL_ACTIVE_ATTRIBUTES*/);
-          ptable.maxAttributeLength = 0; // Spec says if there are no active attribs, 0 must be returned.
-          for (var i = 0; i < numAttribs; ++i) {
-            var activeAttrib = GLctx.getActiveAttrib(program, i);
-            ptable.maxAttributeLength = Math.max(ptable.maxAttributeLength, activeAttrib.name.length+1);
+        if (!program.maxAttributeLength) {
+          for (var i = 0; i < GLctx.getProgramParameter(program, 0x8B89/*GL_ACTIVE_ATTRIBUTES*/); ++i) {
+            program.maxAttributeLength = Math.max(program.maxAttributeLength, GLctx.getActiveAttrib(program, i).name.length+1);
           }
         }
-        HEAP32[((p)>>2)] = ptable.maxAttributeLength;
+        HEAP32[((p)>>2)] = program.maxAttributeLength;
       } else if (pname == 0x8A35 /* GL_ACTIVE_UNIFORM_BLOCK_MAX_NAME_LENGTH */) {
-        if (ptable.maxUniformBlockNameLength == -1) {
-          program = GL.programs[program];
-          var numBlocks = GLctx.getProgramParameter(program, 0x8A36/*GL_ACTIVE_UNIFORM_BLOCKS*/);
-          ptable.maxUniformBlockNameLength = 0;
-          for (var i = 0; i < numBlocks; ++i) {
-            var activeBlockName = GLctx.getActiveUniformBlockName(program, i);
-            ptable.maxUniformBlockNameLength = Math.max(ptable.maxUniformBlockNameLength, activeBlockName.length+1);
+        if (!program.maxUniformBlockNameLength) {
+          for (var i = 0; i < GLctx.getProgramParameter(program, 0x8A36/*GL_ACTIVE_UNIFORM_BLOCKS*/); ++i) {
+            program.maxUniformBlockNameLength = Math.max(program.maxUniformBlockNameLength, GLctx.getActiveUniformBlockName(program, i).length+1);
           }
         }
-        HEAP32[((p)>>2)] = ptable.maxUniformBlockNameLength;
+        HEAP32[((p)>>2)] = program.maxUniformBlockNameLength;
       } else {
-        HEAP32[((p)>>2)] = GLctx.getProgramParameter(GL.programs[program], pname);
+        HEAP32[((p)>>2)] = GLctx.getProgramParameter(program, pname);
       }
     }
 
@@ -2728,27 +2708,91 @@ var ASM_CONSTS = {
       return parseInt(str);
     }
   function _glGetUniformLocation(program, name) {
+      // Returns the index of '[' character in an uniform that represents an array of uniforms (e.g. colors[10])
+      // Closure does counterproductive inlining: https://github.com/google/closure-compiler/issues/3203, so prevent
+      // inlining manually.
+      /** @noinline */
+      function getLeftBracePos(name) {
+        return name.slice(-1) == ']' && name.lastIndexOf('[');
+      }
+  
       name = UTF8ToString(name);
   
+      program = GL.programs[program];
+      var uniformLocsById = program.uniformLocsById; // Maps GLuint -> WebGLUniformLocation
+      var uniformSizeAndIdsByName = program.uniformSizeAndIdsByName; // Maps name -> [uniform array length, GLuint]
+      var i, j;
       var arrayIndex = 0;
+      var uniformBaseName = name;
+  
+      // Invariant: when populating integer IDs for uniform locations, we must maintain the precondition that
+      // arrays reside in contiguous addresses, i.e. for a 'vec4 colors[10];', colors[4] must be at location colors[0]+4.
+      // However, user might call glGetUniformLocation(program, "colors") for an array, so we cannot discover based on the user
+      // input arguments whether the uniform we are dealing with is an array. The only way to discover which uniforms are arrays
+      // is to enumerate over all the active uniforms in the program.
+      var leftBrace = getLeftBracePos(name);
+  
+      // On the first time invocation of glGetUniformLocation on this shader program:
+      // initialize cache data structures and discover which uniforms are arrays.
+      if (!uniformLocsById) {
+        // maps GLint integer locations to WebGLUniformLocations
+        program.uniformLocsById = uniformLocsById = {};
+        // maps integer locations back to uniform name strings, so that we can lazily fetch uniform array locations
+        program.uniformArrayNamesById = {};
+  
+        for (i = 0; i < GLctx.getProgramParameter(program, 0x8B86/*GL_ACTIVE_UNIFORMS*/); ++i) {
+          var u = GLctx.getActiveUniform(program, i);
+          var nm = u.name;
+          var sz = u.size;
+          var lb = getLeftBracePos(nm);
+          var arrayName = lb > 0 ? nm.slice(0, lb) : nm;
+  
+          // Assign a new location.
+          var id = program.uniformIdCounter;
+          program.uniformIdCounter += sz;
+          // Eagerly get the location of the uniformArray[0] base element.
+          // The remaining indices >0 will be left for lazy evaluation to
+          // improve performance. Those may never be needed to fetch, if the
+          // application fills arrays always in full starting from the first
+          // element of the array.
+          uniformSizeAndIdsByName[arrayName] = [sz, id];
+  
+          // Store placeholder integers in place that highlight that these
+          // >0 index locations are array indices pending population.
+          for(j = 0; j < sz; ++j) {
+            uniformLocsById[id] = j;
+            program.uniformArrayNamesById[id++] = arrayName;
+          }
+        }
+      }
+  
       // If user passed an array accessor "[index]", parse the array index off the accessor.
-      if (name[name.length - 1] == ']') {
-        var leftBrace = name.lastIndexOf('[');
-        arrayIndex = name[leftBrace+1] != ']' ? jstoi_q(name.slice(leftBrace + 1)) : 0; // "index]", parseInt will ignore the ']' at the end; but treat "foo[]" as "foo[0]"
-        name = name.slice(0, leftBrace);
+      if (leftBrace > 0) {
+        arrayIndex = jstoi_q(name.slice(leftBrace + 1)) >>> 0; // "index]", coerce parseInt(']') with >>>0 to treat "foo[]" as "foo[0]" and foo[-1] as unsigned out-of-bounds.
+        uniformBaseName = name.slice(0, leftBrace);
       }
   
-      var uniformInfo = GL.programInfos[program] && GL.programInfos[program].uniforms[name]; // returns pair [ dimension_of_uniform_array, uniform_location ]
-      if (uniformInfo && arrayIndex >= 0 && arrayIndex < uniformInfo[0]) { // Check if user asked for an out-of-bounds element, i.e. for 'vec4 colors[3];' user could ask for 'colors[10]' which should return -1.
-        return uniformInfo[1] + arrayIndex;
-      } else {
-        return -1;
+      // Have we cached the location of this uniform before?
+      var sizeAndId = uniformSizeAndIdsByName[uniformBaseName]; // A pair [array length, GLint of the uniform location]
+  
+      // If an uniform with this name exists, and if its index is within the array limits (if it's even an array),
+      // query the WebGLlocation, or return an existing cached location.
+      if (sizeAndId && arrayIndex < sizeAndId[0]) {
+        arrayIndex += sizeAndId[1]; // Add the base location of the uniform to the array index offset.
+        if ((uniformLocsById[arrayIndex] = uniformLocsById[arrayIndex] || GLctx.getUniformLocation(program, name))) {
+          return arrayIndex;
+        }
       }
+      return -1;
     }
 
   function _glLinkProgram(program) {
-      GLctx.linkProgram(GL.programs[program]);
-      GL.populateUniformTable(program);
+      program = GL.programs[program];
+      GLctx.linkProgram(program);
+      // Invalidate earlier computed uniform->ID mappings, those have now become stale
+      program.uniformLocsById = 0; // Mark as null-like so that glGetUniformLocation() knows to populate this again.
+      program.uniformSizeAndIdsByName = {};
+  
     }
 
   function _glShaderSource(shader, count, string, length) {
@@ -2757,11 +2801,25 @@ var ASM_CONSTS = {
       GLctx.shaderSource(GL.shaders[shader], source);
     }
 
+  function webglGetUniformLocation(location) {
+      var p = GLctx.currentProgram;
+      var webglLoc = p.uniformLocsById[location];
+      // p.uniformLocsById[location] stores either an integer, or a WebGLUniformLocation.
+  
+      // If an integer, we have not yet bound the location, so do it now. The integer value specifies the array index
+      // we should bind to.
+      if (webglLoc >= 0) {
+        p.uniformLocsById[location] = webglLoc = GLctx.getUniformLocation(p, p.uniformArrayNamesById[location] + (webglLoc > 0 ? '[' + webglLoc + ']' : ''));
+      }
+      // Else an already cached WebGLUniformLocation, return it.
+      return webglLoc;
+    }
+  
   var miniTempWebGLFloatBuffers=[];
   function _glUniformMatrix4fv(location, count, transpose, value) {
   
       if (GL.currentContext.version >= 2) { // WebGL 2 provides new garbage-free entry points to call to WebGL. Use those always when possible.
-        GLctx.uniformMatrix4fv(GL.uniforms[location], !!transpose, HEAPF32, value>>2, count*16);
+        GLctx.uniformMatrix4fv(webglGetUniformLocation(location), !!transpose, HEAPF32, value>>2, count*16);
         return;
       }
   
@@ -2794,11 +2852,15 @@ var ASM_CONSTS = {
       {
         var view = HEAPF32.subarray((value)>>2, (value+count*64)>>2);
       }
-      GLctx.uniformMatrix4fv(GL.uniforms[location], !!transpose, view);
+      GLctx.uniformMatrix4fv(webglGetUniformLocation(location), !!transpose, view);
     }
 
   function _glUseProgram(program) {
-      GLctx.useProgram(GL.programs[program]);
+      program = GL.programs[program];
+      GLctx.useProgram(program);
+      // Record the currently active program so that we can access the uniform
+      // mapping table of that program.
+      GLctx.currentProgram = program;
     }
 
   function _glVertexAttribPointer(index, size, type, normalized, stride, ptr) {
@@ -3010,6 +3072,10 @@ if (!Object.getOwnPropertyDescriptor(Module, "ENV")) Module["ENV"] = function()
 if (!Object.getOwnPropertyDescriptor(Module, "ERRNO_CODES")) Module["ERRNO_CODES"] = function() { abort("'ERRNO_CODES' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
 if (!Object.getOwnPropertyDescriptor(Module, "ERRNO_MESSAGES")) Module["ERRNO_MESSAGES"] = function() { abort("'ERRNO_MESSAGES' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
 if (!Object.getOwnPropertyDescriptor(Module, "setErrNo")) Module["setErrNo"] = function() { abort("'setErrNo' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
+if (!Object.getOwnPropertyDescriptor(Module, "inetPton4")) Module["inetPton4"] = function() { abort("'inetPton4' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
+if (!Object.getOwnPropertyDescriptor(Module, "inetNtop4")) Module["inetNtop4"] = function() { abort("'inetNtop4' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
+if (!Object.getOwnPropertyDescriptor(Module, "inetPton6")) Module["inetPton6"] = function() { abort("'inetPton6' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
+if (!Object.getOwnPropertyDescriptor(Module, "inetNtop6")) Module["inetNtop6"] = function() { abort("'inetNtop6' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
 if (!Object.getOwnPropertyDescriptor(Module, "readSockaddr")) Module["readSockaddr"] = function() { abort("'readSockaddr' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
 if (!Object.getOwnPropertyDescriptor(Module, "writeSockaddr")) Module["writeSockaddr"] = function() { abort("'writeSockaddr' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
 if (!Object.getOwnPropertyDescriptor(Module, "DNS")) Module["DNS"] = function() { abort("'DNS' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
@@ -3033,7 +3099,12 @@ if (!Object.getOwnPropertyDescriptor(Module, "dynCallLegacy")) Module["dynCallLe
 if (!Object.getOwnPropertyDescriptor(Module, "getDynCaller")) Module["getDynCaller"] = function() { abort("'getDynCaller' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
 if (!Object.getOwnPropertyDescriptor(Module, "dynCall")) Module["dynCall"] = function() { abort("'dynCall' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
 if (!Object.getOwnPropertyDescriptor(Module, "callRuntimeCallbacks")) Module["callRuntimeCallbacks"] = function() { abort("'callRuntimeCallbacks' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
-if (!Object.getOwnPropertyDescriptor(Module, "abortStackOverflow")) Module["abortStackOverflow"] = function() { abort("'abortStackOverflow' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
+if (!Object.getOwnPropertyDescriptor(Module, "runtimeKeepaliveCounter")) Module["runtimeKeepaliveCounter"] = function() { abort("'runtimeKeepaliveCounter' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
+if (!Object.getOwnPropertyDescriptor(Module, "keepRuntimeAlive")) Module["keepRuntimeAlive"] = function() { abort("'keepRuntimeAlive' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
+if (!Object.getOwnPropertyDescriptor(Module, "runtimeKeepalivePush")) Module["runtimeKeepalivePush"] = function() { abort("'runtimeKeepalivePush' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
+if (!Object.getOwnPropertyDescriptor(Module, "runtimeKeepalivePop")) Module["runtimeKeepalivePop"] = function() { abort("'runtimeKeepalivePop' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
+if (!Object.getOwnPropertyDescriptor(Module, "callUserCallback")) Module["callUserCallback"] = function() { abort("'callUserCallback' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
+if (!Object.getOwnPropertyDescriptor(Module, "maybeExit")) Module["maybeExit"] = function() { abort("'maybeExit' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
 if (!Object.getOwnPropertyDescriptor(Module, "reallyNegative")) Module["reallyNegative"] = function() { abort("'reallyNegative' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
 if (!Object.getOwnPropertyDescriptor(Module, "unSign")) Module["unSign"] = function() { abort("'unSign' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
 if (!Object.getOwnPropertyDescriptor(Module, "reSign")) Module["reSign"] = function() { abort("'reSign' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
@@ -3134,6 +3205,7 @@ if (!Object.getOwnPropertyDescriptor(Module, "emscriptenWebGLGet")) Module["emsc
 if (!Object.getOwnPropertyDescriptor(Module, "computeUnpackAlignedImageSize")) Module["computeUnpackAlignedImageSize"] = function() { abort("'computeUnpackAlignedImageSize' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
 if (!Object.getOwnPropertyDescriptor(Module, "emscriptenWebGLGetTexPixelData")) Module["emscriptenWebGLGetTexPixelData"] = function() { abort("'emscriptenWebGLGetTexPixelData' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
 if (!Object.getOwnPropertyDescriptor(Module, "emscriptenWebGLGetUniform")) Module["emscriptenWebGLGetUniform"] = function() { abort("'emscriptenWebGLGetUniform' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
+if (!Object.getOwnPropertyDescriptor(Module, "webglGetUniformLocation")) Module["webglGetUniformLocation"] = function() { abort("'webglGetUniformLocation' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
 if (!Object.getOwnPropertyDescriptor(Module, "emscriptenWebGLGetVertexAttrib")) Module["emscriptenWebGLGetVertexAttrib"] = function() { abort("'emscriptenWebGLGetVertexAttrib' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
 if (!Object.getOwnPropertyDescriptor(Module, "emscriptenWebGLGetBufferBinding")) Module["emscriptenWebGLGetBufferBinding"] = function() { abort("'emscriptenWebGLGetBufferBinding' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
 if (!Object.getOwnPropertyDescriptor(Module, "emscriptenWebGLValidateMapBufferTarget")) Module["emscriptenWebGLValidateMapBufferTarget"] = function() { abort("'emscriptenWebGLValidateMapBufferTarget' was not exported. add it to EXTRA_EXPORTED_RUNTIME_METHODS (see the FAQ)") };
@@ -3223,7 +3295,6 @@ function callMain(args) {
       return;
     } else if (e == 'unwind') {
       // running an evented main loop, don't immediately exit
-      noExitRuntime = true;
       return;
     } else {
       var toLog = e;
@@ -3333,17 +3404,19 @@ function checkUnflushedContent() {
 
 /** @param {boolean|number=} implicit */
 function exit(status, implicit) {
+  EXITSTATUS = status;
+
   checkUnflushedContent();
 
   // if this is just main exit-ing implicitly, and the status is 0, then we
   // don't need to do anything here and can just leave. if the status is
   // non-zero, though, then we need to report it.
   // (we may have warned about this earlier, if a situation justifies doing so)
-  if (implicit && noExitRuntime && status === 0) {
+  if (implicit && keepRuntimeAlive() && status === 0) {
     return;
   }
 
-  if (noExitRuntime) {
+  if (keepRuntimeAlive()) {
     // if exit() was called, we may warn the user if the runtime isn't actually being shut down
     if (!implicit) {
       var msg = 'program exited (with status: ' + status + '), but EXIT_RUNTIME is not set, so halting execution but not exiting the runtime or preventing further async execution (build with EXIT_RUNTIME=1, if you want a true shutdown)';
@@ -3351,8 +3424,6 @@ function exit(status, implicit) {
     }
   } else {
 
-    EXITSTATUS = status;
-
     exitRuntime();
 
     if (Module['onExit']) Module['onExit'](status);
diff --git a/2d/rigidbody/rigidbody_1/dist/output.wasm b/2d/rigidbody/rigidbody_1/dist/output.wasm
index c091140..c2fa2dd 100755
--- a/2d/rigidbody/rigidbody_1/dist/output.wasm
+++ b/2d/rigidbody/rigidbody_1/dist/output.wasm
diff --git a/2d/rigidbody/rigidbody_1/main.cpp b/2d/rigidbody/rigidbody_1/main.cpp
index 8d4ab0e..321e3e5 100644
--- a/2d/rigidbody/rigidbody_1/main.cpp
+++ b/2d/rigidbody/rigidbody_1/main.cpp
@@ -11,6 +11,8 @@
 #include <cmath>
 #include <cfloat>
 
+const float32 MAX_VELOCITY = 200.f;
+
 struct Rigidbody {
     Vector2 force = { 0, 0 };
     Vector2 velocity = { 0, 0 };
@@ -35,6 +37,14 @@ struct Rigidbody {
         
         Vector2 acceleration = force / mass;
         velocity += (acceleration * deltaTimeSeconds);
+
+        if (ABS(velocity.x) > MAX_VELOCITY) {
+            velocity.x =  SIGN(velocity.x) * MAX_VELOCITY;
+        }
+        if (ABS(velocity.y) > MAX_VELOCITY) {
+            velocity.y =  SIGN(velocity.y) * MAX_VELOCITY;
+        }
+
         position += (velocity * deltaTimeSeconds);
         force = Vector2 { 0.f, 0.f };
     }
diff --git a/2d/rigidbody/rigidbody_1/snippet1.cpp b/2d/rigidbody/rigidbody_1/snippet1.cpp
new file mode 100644
index 0000000..77a81b7
--- /dev/null
+++ b/2d/rigidbody/rigidbody_1/snippet1.cpp
@@ -0,0 +1,8 @@
+
+struct Rigidbody {
+    Vector2 force = { 0, 0 };
+    Vector2 acceleration = { 0, 0 };
+    Vector2 velocity = { 0, 0 };
+    Vector2 position = { 0, 0 };
+    float32 mass = 1.f;
+};
diff --git a/2d/rigidbody/rigidbody_1/snippet2.cpp b/2d/rigidbody/rigidbody_1/snippet2.cpp
new file mode 100644
index 0000000..8ad468c
--- /dev/null
+++ b/2d/rigidbody/rigidbody_1/snippet2.cpp
@@ -0,0 +1,25 @@
+
+
+struct Rigidbody {
+    Vector2 force = { 0, 0 };
+    Vector2 velocity = { 0, 0 };
+    Vector2 position = { 0, 0 };
+    float32 mass = 1.f;
+
+    void applyForce(Vector2 f) {
+        force += f;
+    }
+
+    void applyGravity(float32 deltaTimeSeconds) {
+        velocity += (Vector2 { 0.f, -50.f } * deltaTimeSeconds);
+    }
+
+    void update(float32 deltaTimeSeconds) {
+        applyGravity(deltaTimeSeconds);
+        
+        Vector2 acceleration = force / mass;
+        velocity += (acceleration * deltaTimeSeconds);
+        position += (velocity * deltaTimeSeconds);
+        force = Vector2 { 0.f, 0.f };
+    }
+};