use delta in update_particles(), init times, misc cleanups

1 files changed, 19 insertions, 13 deletions

diff --git a/main.c b/main.c
index 04eb4ce..e4bd106 100644
--- a/main.c
+++ b/main.c
@@ -97,9 +97,11 @@ cs_src[] =
   "\n"
   PARTICLE_BUFFER
   "\n"
+  "uniform mediump float delta;\n"
+  "\n"
   "void main() {\n"
   "  mediump uint i = gl_GlobalInvocationID.x;\n"
-  "  positions[i] += 0.016 * velocities[i];\n"
+  "  positions[i].xy += delta * velocities[i].xy;\n"
   "\n"
   "  if (positions[i].x > 1.1) {\n"
   "    positions[i].x -= 2.2;\n"
@@ -359,16 +361,20 @@ init_particles(void) {
 static void
 update_particles(
   const GLuint ssbo,
-  const GLuint compute_prog
+  const GLuint compute_prog,
+  const GLint u_delta,
+  const float delta
 ) {
   if (USE_COMPUTE_SHADER) {
     UNUSED(ssbo);
 
     glUseProgram(compute_prog);
+    glUniform1f(u_delta, delta);
     glDispatchCompute(NUM_PARTICLES / WORKGROUP_SIZE, 1, 1);
     glMemoryBarrier(GL_SHADER_STORAGE_BARRIER_BIT);
   } else {
     UNUSED(compute_prog);
+    UNUSED(u_delta);
 
     // bind shader storage buffer
     glBindBuffer(GL_SHADER_STORAGE_BUFFER, ssbo);
@@ -385,7 +391,7 @@ update_particles(
     #pragma omp parallel for
     for (int i = 0; i < NUM_PARTICLES; i++) {
       // update x coordinate
-      data->positions[4 * i + 0] += 0.016 * data->velocities[4 * i + 0];
+      data->positions[4 * i + 0] += delta * data->velocities[4 * i + 0];
       if (data->positions[4 * i + 0] < -1.1) {
         data->positions[4 * i + 0] += 2.2;
       } else if (data->positions[4 * i + 0] > 1.1) {
@@ -393,7 +399,7 @@ update_particles(
       }
 
       // update y coordinate
-      data->positions[4 * i + 1] += 0.016 * data->velocities[4 * i + 1];
+      data->positions[4 * i + 1] += delta * data->velocities[4 * i + 1];
       if (data->positions[4 * i + 1] < -1.1) {
         data->positions[4 * i + 1] += 2.2;
       } else if (data->positions[4 * i + 1] > 1.1) {
@@ -535,7 +541,7 @@ ctx_init(context_t * const ctx) {
   }
 
   // init times ring buffer
-  // memset(ctx->times, 0, sizeof(ctx->times));
+  memset(ctx->times, 0, sizeof(ctx->times));
   ctx->times_ofs = 0;
 
   // init flags
@@ -669,26 +675,26 @@ int main(int argc, char *argv[]) {
   // unbind vao
   glBindVertexArray(0);
 
-  // link compute program
+  // link compute program, get uniform
   GLuint compute_prog = link_program(1, COMPUTE_SHADERS);
-  // TODO: need to pass delta in shader storage block eventually
-  // (for now it's hard-coded as 16ms in shader)
-  // GLint u_delta = glGetUniformLocation(compute_prog, "delta");
+  GLint u_delta = glGetUniformLocation(compute_prog, "delta");
 
-  // link render program, get uniforms
+  // link render program, get uniform
   GLuint render_prog = link_program(2, RENDER_SHADERS);
   GLint u_time = glGetUniformLocation(render_prog, "time");
 
   // main loop
   while (!ctx.done) {
-    // get start time
-    uint32_t now = SDL_GetTicks();
+    // get start time, then calculate delta
+    const uint32_t now = SDL_GetTicks();
+    const uint32_t last_times_ofs = (ctx.times_ofs - 1) & (MAX_TIMES - 1);
+    const float delta = (now - ctx.times[last_times_ofs].draw_start) / 1000.0;
 
     // save start time
     ctx.times[ctx.times_ofs].draw_start = now;
 
     // update particles
-    update_particles(ssbo, compute_prog);
+    update_particles(ssbo, compute_prog, u_delta, delta);
 
     // clear screen
     glClearColor(0, 0, 0, 1);