add update_particles() and USE_COMPUTE_SHADER

1 files changed, 120 insertions, 72 deletions

diff --git a/main.c b/main.c
index 49ca8e2..6f620b5 100644
--- a/main.c
+++ b/main.c
@@ -17,7 +17,13 @@
 // custom SDL_USEREVENT code for timer
 #define EVENT_CODE_TIMER 0
 
+// use compute shader to update particles?
+#define USE_COMPUTE_SHADER false
+
+// number of particles
 #define NUM_PARTICLES 1000
+
+// number of compute shader workgroups
 #define WORKGROUP_SIZE 1
 
 typedef struct {
@@ -100,7 +106,8 @@ fs_src[] =
   "uniform mediump float time;\n"
   "\n"
   "void main() {\n"
-  "  color = vec4(colors[instance_id].rgb, 1) * (0.5f + 0.5 * sin(time * 3.141));\n"
+  "  mediump float alpha = 0.5f + 0.5f * (0.5f + 0.5 * sin(time * 3.141));\n"
+  "  color = vec4(colors[instance_id].rgb, 1) * alpha;\n"
   "}\n";
 
 static const shader_t
@@ -183,6 +190,113 @@ link_program(
   return r;
 }
 
+static float
+color_map(uint8_t bits) {
+  switch (bits & 0x3) {
+  case 0x3:
+    return 1.0;
+  case 0x2:
+    return 0.75;
+  case 0x1:
+    return 0.5;
+  default:
+    return 0.25;
+  }
+}
+
+static GLuint
+init_particles(void) {
+  // create shader storage buffer
+  GLuint ssbo;
+  glGenBuffers(1, &ssbo);
+
+  // generate seed data
+  uint8_t seeds[5 * NUM_PARTICLES];
+  if (!RAND_bytes(seeds, 5 * NUM_PARTICLES)) {
+    SDL_Log("RAND_bytes() failed");
+    exit(EXIT_FAILURE);
+  }
+
+  // populate data
+  float data[3 * 4 * NUM_PARTICLES];
+  #pragma omp parallel for
+  for (int i = 0; i < NUM_PARTICLES; i++) {
+    float x = 2.0 * seeds[5 * i + 0] / 0xFF - 1.0,
+          y = 2.0 * seeds[5 * i + 1] / 0xFF - 1.0;
+
+    // SDL_Log("%f,%f", x, y);
+
+    // populate position
+    data[4 * i + 0] = x;
+    data[4 * i + 1] = y;
+    data[4 * i + 2] = 0.0;
+    data[4 * i + 3] = 1.0;
+
+    // populate random velocity
+    data[4 * (NUM_PARTICLES + i) + 0] = 2.0 * seeds[5 * i + 2] / 0xFF - 1.0;
+    data[4 * (NUM_PARTICLES + i) + 1] = 2.0 * seeds[5 * i + 3] / 0xFF - 1.0;
+
+    // populate colors
+    uint8_t cs = seeds[5 * i + 4];
+    data[4 * (2 * NUM_PARTICLES + i) + 0] = color_map(cs & 0x3);
+    data[4 * (2 * NUM_PARTICLES + i) + 1] = color_map((cs >> 2) & 0x3);
+    data[4 * (2 * NUM_PARTICLES + i) + 2] = color_map((cs >> 4) & 0x3);
+    data[4 * (2 * NUM_PARTICLES + i) + 3] = 1.0;
+  }
+
+  // populate buffer
+  glBindBuffer(GL_SHADER_STORAGE_BUFFER, ssbo);
+  glBufferData(GL_SHADER_STORAGE_BUFFER, sizeof(data), data, GL_DYNAMIC_DRAW);
+  glBindBuffer(GL_SHADER_STORAGE_BUFFER, 0);
+
+  // return buffer
+  return ssbo;
+}
+
+static void
+update_particles(
+  const GLuint ssbo,
+  const GLuint compute_prog
+) {
+  if (USE_COMPUTE_SHADER) {
+    UNUSED(ssbo);
+    glUseProgram(compute_prog);
+    glDispatchCompute(NUM_PARTICLES / WORKGROUP_SIZE, 1, 1);
+    glMemoryBarrier(GL_SHADER_STORAGE_BARRIER_BIT);
+  } else {
+    UNUSED(compute_prog);
+    glBindBuffer(GL_SHADER_STORAGE_BUFFER, ssbo);
+
+    // map buffer
+    float *data = glMapBufferRange(
+      GL_SHADER_STORAGE_BUFFER,
+      0,
+      3 * NUM_PARTICLES * 4 * sizeof(float),
+      GL_MAP_READ_BIT | GL_MAP_WRITE_BIT
+    );
+
+    #pragma omp parallel for
+    for (int i = 0; i < NUM_PARTICLES; i++) {
+      data[4 * i + 0] += 0.016 * data[4 * (NUM_PARTICLES + i) + 0];
+      if (data[4 * i + 0] < -1.1) {
+        data[4 * i + 0] += 2.2;
+      } else if (data[4 * i + 0] > 1.1) {
+        data[4 * i + 0] -= 2.2;
+      }
+
+      data[4 * i + 1] += 0.016 * data[4 * (NUM_PARTICLES + i) + 1];
+      if (data[4 * i + 1] < -1.1) {
+        data[4 * i + 1] += 2.2;
+      } else if (data[4 * i + 1] > 1.1) {
+        data[4 * i + 1] -= 2.2;
+      }
+    }
+
+    glUnmapBuffer(GL_SHADER_STORAGE_BUFFER);
+    glBindBuffer(GL_SHADER_STORAGE_BUFFER, 0);
+  }
+}
+
 static void
 update_viewport(
   SDL_Window *win
@@ -350,7 +464,8 @@ handle_events(
   }
 }
 
-static Uint32 timer_cb(
+static Uint32
+timer_cb(
   Uint32 interval,
   void *arg
 ) {
@@ -371,69 +486,6 @@ static Uint32 timer_cb(
   return interval;
 }
 
-static float
-color_map(uint8_t bits) {
-  switch (bits & 0x3) {
-  case 0x3:
-    return 1.0;
-  case 0x2:
-    return 0.75;
-  case 0x1:
-    return 0.5;
-  default:
-    return 0.25;
-  }
-}
-
-static GLuint
-init_particles(void) {
-  // create shader storage buffer
-  GLuint ssbo;
-  glGenBuffers(1, &ssbo);
-
-  // generate seed data
-  uint8_t seeds[5 * NUM_PARTICLES];
-  if (!RAND_bytes(seeds, 5 * NUM_PARTICLES)) {
-    SDL_Log("RAND_bytes() failed");
-    exit(EXIT_FAILURE);
-  }
-
-  // populate data
-  float data[3 * 4 * NUM_PARTICLES];
-  #pragma omp parallel for
-  for (int i = 0; i < NUM_PARTICLES; i++) {
-    float x = 2.0 * seeds[5 * i + 0] / 0xFF - 1.0,
-          y = 2.0 * seeds[5 * i + 1] / 0xFF - 1.0;
-
-    // SDL_Log("%f,%f", x, y);
-
-    // populate position
-    data[4 * i + 0] = x;
-    data[4 * i + 1] = y;
-    data[4 * i + 2] = 0.0;
-    data[4 * i + 3] = 1.0;
-
-    // populate random velocity
-    data[4 * (NUM_PARTICLES + i) + 0] = 2.0 * seeds[5 * i + 2] / 0xFF - 1.0;
-    data[4 * (NUM_PARTICLES + i) + 1] = 2.0 * seeds[5 * i + 3] / 0xFF - 1.0;
-
-    // populate colors
-    uint8_t cs = seeds[5 * i + 4];
-    data[4 * (2 * NUM_PARTICLES + i) + 0] = color_map(cs & 0x3);
-    data[4 * (2 * NUM_PARTICLES + i) + 1] = color_map((cs >> 2) & 0x3);
-    data[4 * (2 * NUM_PARTICLES + i) + 2] = color_map((cs >> 4) & 0x3);
-    data[4 * (2 * NUM_PARTICLES + i) + 3] = 1.0;
-  }
-
-  // populate buffer
-  glBindBuffer(GL_SHADER_STORAGE_BUFFER, ssbo);
-  glBufferData(GL_SHADER_STORAGE_BUFFER, sizeof(data), data, GL_STATIC_DRAW);
-  glBindBuffer(GL_SHADER_STORAGE_BUFFER, 0);
-
-  // return buffer
-  return ssbo;
-}
-
 int main(int argc, char *argv[]) {
   UNUSED(argc);
   UNUSED(argv);
@@ -466,7 +518,7 @@ int main(int argc, char *argv[]) {
   // unbind vao
   glBindVertexArray(0);
 
-  // link compute program, get uniforms
+  // link compute program
   GLuint compute_prog = link_program(1, COMPUTE_SHADERS);
   // GLint u_delta = glGetUniformLocation(compute_prog, "delta");
 
@@ -482,12 +534,8 @@ int main(int argc, char *argv[]) {
     // save start time
     ctx.times[ctx.times_ofs].draw_start = now;
 
-    // disabled, crashing
-/* 
- *     glUseProgram(compute_prog);
- *     glDispatchCompute(NUM_PARTICLES / WORKGROUP_SIZE, 1, 1);
- *     glMemoryBarrier(GL_SHADER_STORAGE_BARRIER_BIT);
- */ 
+    // update particles
+    update_particles(ssbo, compute_prog);
 
     // clear screen
     glClearColor(0, 0, 0, 1);