boilerplate in shader reduction

fragment.glsl

@@ -1,9 +1,3 @@
-#version 330 core
-
-uniform vec2 WindowSize;
-uniform float time;
-layout(location = 0) out vec4 color;
-
 float lerp(float a, float b, float x) {
     return a + x*(b-a);
 }
@@ -73,19 +67,20 @@ float limit(float val, float min, float max) {
     return out_val;
 }
 
-void main() {
-    vec2 screen_uv = gl_FragCoord.xy / WindowSize;
+void mainImage(out vec4 fragColor, in vec2 fragCoord) {
+    vec2 screen_uv = gl_FragCoord.xy / iResolution;
     // We'll make origin in the top-left.
     screen_uv.y = 1.0 - screen_uv.y;
-    screen_uv.x *= WindowSize.x / WindowSize.y;
+    screen_uv.x *= iResolution.x / iResolution.y;
     vec2 uv = vec2(screen_uv.x, screen_uv.y);
-    uv.y += sin(uv.x * 2.0 + time * 0.2) * 0.47;
-    uv.y += sin(uv.x * 4.3 + time * 1.34) * 0.09;
+    uv.y += sin(uv.x * 2.0 + iTime * 0.2) * 0.47;
+    uv.y += sin(uv.x * 4.3 + iTime * 1.34) * 0.09;
 
     uv += 100.0;
-    float out_val = perlin_noise(uv, vec2(0.0, 0.0), time / 1.0);
-    float min = 0.42 + sin(time)/8.0;
-    float max = 0.58 + sin(time)/8.0;
+    float out_val = perlin_noise(uv, vec2(0.0, 0.0), iTime / 1.0);
+    float min = 0.42 + sin(iTime)/8.0;
+    float max = 0.58 + sin(iTime)/8.0;
     out_val = limit(out_val, min, max);
-    color = vec4(out_val, 0.4, 0.8, 1.0);
+    fragColor = vec4(out_val, 0.4, 0.8, 1.0);
 }
+

renderer.c

@@ -28,7 +28,7 @@ GLuint compile_shader(GLuint type, const char *src) {
 }
 
 const char *vertex_shader_src =
-"#version 330 core\n"
+"#version 300 es\n"
 "\n"
 "layout(location = 0) in vec2 aPos;\n"
 "\n"
@@ -36,6 +36,21 @@ const char *vertex_shader_src =
 "    gl_Position = vec4(aPos, 0.0, 1.0);\n"
 "}\n";
 
+const char *fragment_header_src = 
+"#version 300 es\n"
+"precision highp float;\n"
+"precision highp int;\n"
+"precision lowp sampler2D;\n"
+"precision lowp samplerCube;\n"
+"layout(location = 0) out vec4 color;\n"
+"uniform vec2 iResolution;\n"
+"uniform float iTime;\n"
+"void mainImage(out vec4 fragColor, in vec2 fragCoord);\n"
+"void main() {\n"
+"   mainImage(color, gl_FragCoord.xy);\n"
+"}\n"
+"\n";
+
 /// returns 0 if failed.
 GLuint create_shader(const char *fragment_src) {
     GLuint program = glCreateProgram();
@@ -60,14 +75,24 @@ GLuint load_shader(const char *path) {
         printf("failed to open shader file: '%s'\n", path);
         exit(1);
     }
+
     fseek(handle, 0L, SEEK_END);
-    long length = ftell(handle);
+    long file_length = ftell(handle);
     fseek(handle, 0L, SEEK_SET);
+
+    long header_length = strlen(fragment_header_src);
+    long length = header_length + file_length;
+
     char *string = malloc((length + 1) * sizeof(char));
-    if (!fread(string, sizeof(char), length, handle)) {
+
+    // Copy header.
+    strcpy(string, fragment_header_src);
+
+    if (!fread(string + header_length, sizeof(char), file_length, handle)) {
         printf("failed to read shader file\n");
         exit(1);
     }
+
     // I love C
     string[length] = '\0';
     fclose(handle);
@@ -164,11 +189,11 @@ void render(Renderer *state, int w, int h, double time, char *shader_path, int r
     // Shader parameters.
     glUseProgram(state->shader);
 
-    int uniform_WindowSize = glGetUniformLocation(state->shader, "WindowSize");
-    glUniform2f(uniform_WindowSize, w, h);
+    int uniform_iResolution = glGetUniformLocation(state->shader, "iResolution");
+    glUniform2f(uniform_iResolution, w, h);
 
-    int uniform_time = glGetUniformLocation(state->shader, "time");
-    glUniform1f(uniform_time, (float)time);
+    int uniform_iTime = glGetUniformLocation(state->shader, "iTime");
+    glUniform1f(uniform_iTime, (float)time);
 
     glBindVertexArray(state->vao);
     glDrawArrays(GL_TRIANGLES, 0, 6);