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#include "../../../shared_cpp/Renderer2d.h"
#include "../../../shared_cpp/types.h"
#include "../../../shared_cpp/mathlib.h"
struct PointMassUpdateData {
int32 index = 0;
Vector2 restingPosition; // Position is in world coordinates
Vector2 currentPosition; // Position is in world coordinates
Vector2 velocity;
Vector2 acceleration;
Vector2 force;
bool isHovered = false;
PointMassUpdateData* neighbors[4];
};
struct SoftbodyRectangle {
// User defined
float32 width = 200;
float32 height = 200;
int32 springDensity = 16;
float32 k = 10000000.f; // in N /m
float32 c = 9000.f;
float32 jointMassKg = 10.f;
float32 floorPosition = 0;
// Calculated before runtime
Vector2 springDimensions;
// Runtime data
PointMassUpdateData* updateData = NULL;
// Render data
Mesh2d mesh;
Mesh2d pointsMesh;
Mesh2d floorMesh;
Vertex2d* vertices = NULL;
Vertex2d* pointsVertices = NULL;
void load(Renderer2d* renderer) {
auto defaultPosition = Vector2(800 / 2 - width / 2, 400);
springDimensions = Vector2(width / springDensity, height / springDensity);
int32 numVertices = springDensity * springDensity; // Each subdivision is a square.
int32 numIndices = 6 * ((springDensity - 1) * (springDensity - 1));
vertices = new Vertex2d[numVertices];
updateData = new PointMassUpdateData[numVertices];
pointsVertices = new Vertex2d[numVertices];
auto indices = new GLuint[numIndices];
// -- Load a square with the desired density
int32 vIdx = 0;
int32 iIdx = 0;
float32 inverseDensity = 1.f / springDensity;
float32 halfInv = inverseDensity / 2.f;
for (int32 y = 0; y < springDensity; y++) { // Rows
for (int32 x = 0; x < springDensity; x++) { // Columns
Vector2 vpos = Vector2(x * inverseDensity - halfInv, y * inverseDensity- halfInv);
vpos.x = vpos.x * width + defaultPosition.x;
vpos.y = vpos.y * height + defaultPosition.y;
vertices[vIdx] = { vpos, Vector4(1, 0, 0, 1) };
updateData[vIdx].index = vIdx;
updateData[vIdx].restingPosition = vpos;
updateData[vIdx].currentPosition = vpos;
updateData[vIdx].force = Vector2(0, 0);
updateData[vIdx].velocity = Vector2(0, 0);
updateData[vIdx].acceleration = Vector2(0, 0);
if (x != springDensity - 1) updateData[vIdx].neighbors[0] = &updateData[vIdx + 1]; // Right
else updateData[vIdx].neighbors[0] = NULL;
if (y != springDensity - 1) updateData[vIdx].neighbors[1] = &updateData[vIdx + springDensity]; // Bottom
else updateData[vIdx].neighbors[1] = NULL;
if (x != 0) updateData[vIdx].neighbors[2] = &updateData[vIdx - 1]; // Left
else updateData[vIdx].neighbors[2] = NULL;
if (y != 0) updateData[vIdx].neighbors[3] = &updateData[vIdx - springDensity]; // Top
else updateData[vIdx].neighbors[3] = NULL;
if (y != springDensity - 1 && x != springDensity - 1) {
indices[iIdx++] = vIdx;
indices[iIdx++] = vIdx + 1;
indices[iIdx++] = vIdx + springDensity;
indices[iIdx++] = vIdx + springDensity;
indices[iIdx++] = vIdx + springDensity + 1;
indices[iIdx++] = vIdx + 1;
}
pointsVertices[vIdx].position = vpos;
pointsVertices[vIdx].color = Vector4(0, 0, 0, 1);
vIdx++;
}
}
mesh.load(vertices, numVertices, indices, numIndices, renderer, GL_DYNAMIC_DRAW);
pointsMesh.load(pointsVertices, numVertices, renderer, GL_DYNAMIC_DRAW);
delete [] indices;
// -- Load the floor line;
Vector2 floorDimensions = Vector2(renderer->context->width, 8);
floorPosition = 100.f;
Vector4 floorColor = Vector4(0.5, 0.5, 0.5, 1);
Vertex2d floorVertices[6];
floorVertices[0] = { Vector4(0, floorPosition, 0, 1), floorColor };
floorVertices[1] = { Vector4(floorDimensions.x, floorPosition, 0, 1), floorColor };
floorVertices[2] = { Vector4(0, floorPosition - floorDimensions.y, 0, 1), floorColor };
floorVertices[3] = { Vector4(0, floorPosition - floorDimensions.y, 0, 1), floorColor };
floorVertices[4] = { Vector4(floorDimensions.x, floorPosition - floorDimensions.y, 0, 1), floorColor };
floorVertices[5] = { Vector4(floorDimensions.x, floorPosition, 0, 1), floorColor };
floorMesh.load(floorVertices, 6, renderer);
}
Vector2 getForceBetweenPointMasses(PointMassUpdateData* first, PointMassUpdateData* second) {
auto relativeVelocity = second->velocity - first->velocity;
auto restLength = (second->restingPosition - first->restingPosition).length();
auto relativePosition = second->currentPosition - first->currentPosition;
auto currentLength = relativePosition.length();
auto positionDir = relativePosition.normalize();
auto velDotProduct = positionDir.dot(relativeVelocity);
auto accelDotProduct = positionDir.dot(second->acceleration - first->acceleration);
float32 springForce = k * (currentLength - restLength);
float32 dampingForce = c * velDotProduct;
float32 accelerationForce = jointMassKg * accelDotProduct;
float32 totalForce = accelerationForce + springForce + dampingForce;
return positionDir * totalForce;
}
void update(float32 dtSeconds) {
for (int32 v = 0; v < pointsMesh.numVertices; v++) {
auto pointMass = &updateData[v];
// -- Add the forces from it's neighbors. Note that we only do the first two
// neighbors, which are the right and bottom neighbors.
for (int32 n = 0; n < 2; n++) {
auto neighbor = pointMass->neighbors[n];
if (neighbor == NULL) continue;
auto forceBetween = getForceBetweenPointMasses(pointMass, neighbor);
pointMass->force = pointMass->force + forceBetween;
neighbor->force = neighbor->force- forceBetween;
}
}
// -- Update the local position of each vertex.
for (int32 v = 0; v < pointsMesh.numVertices; v++) {
auto pointMass = &updateData[v];
auto prevPos = pointMass->currentPosition;
// -- Gravity
Vector2 g = Vector2(0, -9.8 * jointMassKg) * dtSeconds;
// -- Euler integration to find the current velocity and position
pointMass->acceleration = (pointMass->force / jointMassKg) * dtSeconds;
pointMass->velocity = pointMass->velocity + pointMass->acceleration * dtSeconds + g;
pointMass->restingPosition = pointMass->restingPosition + g * dtSeconds;
pointMass->currentPosition = pointMass->currentPosition + (pointMass->velocity * dtSeconds);
pointMass->force = Vector2(0, 0); // Reset the force for the next update
particleFloorCollision(pointMass, prevPos, dtSeconds);
// -- Collision detection
const float32 COLLISION_DISTANCE = 0.3f;
for (int32 n = 0; n < 4; n++) {
auto neighbor = pointMass->neighbors[n];
if (neighbor == NULL) continue;
if ((neighbor->currentPosition - pointMass->currentPosition).length() < COLLISION_DISTANCE) {
auto positionNormal = (neighbor->currentPosition - pointMass->currentPosition).normalize();
pointMass->currentPosition = neighbor->currentPosition - positionNormal * COLLISION_DISTANCE;
float32 dotProduct = pointMass->velocity.dot(positionNormal);
pointMass->velocity = pointMass->velocity - positionNormal * (2 * dotProduct);
}
}
vertices[v].position = pointMass->currentPosition;
pointsVertices[v].position = pointMass->currentPosition;
}
// -- Update vertices
mesh.updateVertices(vertices);
pointsMesh.updateVertices(pointsVertices);
}
void particleFloorCollision(PointMassUpdateData* ud, Vector2 prevPos, float32 dtSeconds) {
// We assume that the floor is always horizontal for this simulation
auto dotProduct = ud->velocity.dot(Vector2(0, 1));
if (dotProduct >= 0) {
return; // Not moving in the same direction
}
if (ud->currentPosition.y - floorPosition < 0.1f) {
// Find the point in the simulation at which we began intersecting, and then reflect.
Vector2 newPosition;
do {
dtSeconds = dtSeconds - 0.02f;
newPosition = prevPos + ud->velocity * dtSeconds;
} while (newPosition.y < floorPosition);
ud->currentPosition = newPosition;
ud->velocity = (ud->velocity - Vector2(0, 1) * (2 * dotProduct)) * 0.5f;
}
}
void render(Renderer2d* renderer) {
mesh.render(renderer);
pointsMesh.render(renderer, GL_POINTS);
floorMesh.render(renderer);
}
void unload() {
mesh.unload();
pointsMesh.unload();
delete [] vertices;
delete [] pointsVertices;
}
};
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