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#include "grass_renderer.hpp"
#include "../renderer_3d.h"
#include "../shader.h"
#include "../shaders/grass_frag.h"
#include "../shaders/grass_vert.h"
#include "mathlib.h"
#include <cmath>
#include <cstddef>
void GrassRenderer::load(GrassRendererLoadData params, Renderer3d *renderer) {
bladeHeight = params.grassHeight;
// Place blades randomly within a circle. Using r = R*sqrt(u) with a
// uniform u in [0,1] gives uniform areal density (no center clustering).
const f32 radius = fminf(params.area.x, params.area.y) * 0.5f;
for (i32 i = 0; i < NUM_GRASS_BLADES; i++) {
f32 r = radius * sqrtf(randomFloatBetween(0.f, 1.f));
f32 theta = randomFloatBetween(0.f, 2.f * PI);
f32 x = params.origin.x + r * cosf(theta);
f32 z = params.origin.y + r * sinf(theta);
grassBlades[i].position = Vector3(x, 0, z);
grassBlades[i].top_offset =
Vector2(randomFloatBetween(0.f, 2.f * PI), // sway phase
randomFloatBetween(0.5f, 1.5f) // height scale
);
}
// Compile grass shader
shader = loadShader(shader_grass_vert, shader_grass_frag);
useShader(shader);
// Attribute locations
attributes.position = getShaderAttribute(shader, "position");
attributes.instancePos = getShaderAttribute(shader, "instancePos");
attributes.instancePhase = getShaderAttribute(shader, "instancePhase");
attributes.instanceHeight = getShaderAttribute(shader, "instanceHeight");
// Uniform locations
uniforms.projection = getShaderUniform(shader, "projection");
uniforms.view = getShaderUniform(shader, "view");
uniforms.time = getShaderUniform(shader, "time");
uniforms.bladeWidth = getShaderUniform(shader, "bladeWidth");
uniforms.bladeHeight = getShaderUniform(shader, "bladeHeight");
uniforms.swayAmount = getShaderUniform(shader, "swayAmount");
// Base quad: two triangles forming a unit quad
// x in [-0.5, 0.5], y in [0, 1]
Vector2 quadVertices[] = {Vector2(-0.5f, 0.0f), Vector2(0.5f, 0.0f),
Vector2(0.5f, 1.0f), Vector2(-0.5f, 0.0f),
Vector2(0.5f, 1.0f), Vector2(-0.5f, 1.0f)};
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
// Static quad VBO
glGenBuffers(1, &quadVbo);
glBindBuffer(GL_ARRAY_BUFFER, quadVbo);
glBufferData(GL_ARRAY_BUFFER, sizeof(quadVertices), quadVertices,
GL_STATIC_DRAW);
glEnableVertexAttribArray(attributes.position);
glVertexAttribPointer(attributes.position, 2, GL_FLOAT, GL_FALSE,
sizeof(Vector2), (GLvoid *)0);
// Dynamic instance VBO
glGenBuffers(1, &instanceVbo);
glBindBuffer(GL_ARRAY_BUFFER, instanceVbo);
glBufferData(GL_ARRAY_BUFFER, NUM_GRASS_BLADES * sizeof(GrassInstanceData),
NULL, GL_DYNAMIC_DRAW);
// instancePos: vec3 (x, y, z) at offset 0
glEnableVertexAttribArray(attributes.instancePos);
glVertexAttribPointer(attributes.instancePos, 3, GL_FLOAT, GL_FALSE,
sizeof(GrassInstanceData),
(GLvoid *)offsetof(GrassInstanceData, x));
glVertexAttribDivisor(attributes.instancePos, 1);
// instancePhase: float at offset 12 (after 3 floats)
glEnableVertexAttribArray(attributes.instancePhase);
glVertexAttribPointer(attributes.instancePhase, 1, GL_FLOAT, GL_FALSE,
sizeof(GrassInstanceData),
(GLvoid *)offsetof(GrassInstanceData, phaseOffset));
glVertexAttribDivisor(attributes.instancePhase, 1);
// instanceHeight: float at offset 16 (after phaseOffset)
glEnableVertexAttribArray(attributes.instanceHeight);
glVertexAttribPointer(attributes.instanceHeight, 1, GL_FLOAT, GL_FALSE,
sizeof(GrassInstanceData),
(GLvoid *)offsetof(GrassInstanceData, heightScale));
glVertexAttribDivisor(attributes.instanceHeight, 1);
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindVertexArray(0);
}
void GrassRenderer::update(f32 dtSeconds) { time += dtSeconds; }
void GrassRenderer::render(Renderer3d *renderer) {
useShader(shader);
setShaderMat4(uniforms.projection, renderer->projection);
setShaderMat4(uniforms.view, renderer->view);
setShaderFloat(uniforms.time, time);
setShaderFloat(uniforms.bladeWidth, bladeWidth);
setShaderFloat(uniforms.bladeHeight, bladeHeight);
setShaderFloat(uniforms.swayAmount, swayAmount);
// Build and upload instance data
GrassInstanceData instanceData[NUM_GRASS_BLADES];
for (i32 i = 0; i < NUM_GRASS_BLADES; i++) {
instanceData[i].x = grassBlades[i].position.x;
instanceData[i].y = grassBlades[i].position.y;
instanceData[i].z = grassBlades[i].position.z;
instanceData[i].phaseOffset = grassBlades[i].top_offset.x;
instanceData[i].heightScale = grassBlades[i].top_offset.y;
}
glBindBuffer(GL_ARRAY_BUFFER, instanceVbo);
glBufferSubData(GL_ARRAY_BUFFER, 0,
NUM_GRASS_BLADES * sizeof(GrassInstanceData), instanceData);
glBindVertexArray(vao);
glDrawArraysInstanced(GL_TRIANGLES, 0, 6, NUM_GRASS_BLADES);
glBindVertexArray(0);
}
void GrassRenderer::unload() {
if (vao)
glDeleteVertexArrays(1, &vao);
if (quadVbo)
glDeleteBuffers(1, &quadVbo);
if (instanceVbo)
glDeleteBuffers(1, &instanceVbo);
if (shader)
glDeleteProgram(shader);
vao = 0;
quadVbo = 0;
instanceVbo = 0;
shader = 0;
}
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