generate noise texture and sample for randomness

shader/root/rt.glsl

@@ -2,6 +2,8 @@
 
 #include sphere.glsl
 
+layout(local_size_x = 1, local_size_y = 1) in;                  // size of local work group - 1 pixel
+
 // TODO: do i actually need explicit location descriptors?
 layout (location = 1)   uniform vec4 _t;
 
@@ -16,14 +18,17 @@ layout (location = 8)   uniform vec3 _camll;
 layout (location = 9)   uniform vec3 _cpos;
 layout (location = 10)  uniform vec3 _tpos;                     // target
 
-const int SPHERES = 250; // 253 is the maximum?? TODO: use uniform buffer objects
+// 253 is the maximum?? TODO: use uniform buffer objects
+const int SPHERES = 250; 
+
 layout (location = 12)  uniform int _activeSpheres;
 layout (location = 13)  uniform Sphere _spheres[SPHERES];
 
 uniform vec4 _seed;
 
-layout(local_size_x = 1, local_size_y = 1) in;                  // size of local work group - 1 pixel
+
 layout(rgba32f, binding = 0) uniform image2D img_output;        // rgba32f defines internal format, image2d for random write to output texture
+layout(binding=1) uniform sampler2D _noise;                     // noise texture
 
 const float INF = 1000.0;
 const float PI = 3.14159;
@@ -144,14 +149,34 @@ RayHit trace(Ray ray)
     return hit;
 }
 
+vec2 pixelUv() 
+{
+    ivec2 pixelCoords = ivec2(gl_GlobalInvocationID.xy);
+
+    ivec2 dims = imageSize(img_output);
+
+    vec2 uv;
+    uv.x = (float(pixelCoords.x * 2 - dims.x) / dims.x) * dims.x/dims.y;       // account for aspect ratio
+    uv.y = (float(pixelCoords.y * 2 - dims.y) / dims.y);
+
+    return uv;
+}
+
+vec4 sampleNoise()
+{
+    return texture(_noise, pixelUv());
+}
+
 float random(vec2 st)
 {
-    st += gl_GlobalInvocationID.xy;
-    st += _seed.xy;
-    st += _seed.zw;
-    normalize(st);
+    //st += gl_GlobalInvocationID.xy;
+    //st += _seed.xy;
+    //st += _seed.zw;
+    //normalize(st);
 
-    return fract(sin(dot(st.xy,vec2(12.9898,78.233)))*43758.5453123);
+    vec2 nuv = texture(_noise, st.xy).xy;
+
+    return fract(sin(dot(nuv,vec2(12.9898,78.233)))*43758.5453123);
 }
 
 float sdot(vec3 x, vec3 y, float f = 1.0)
@@ -173,10 +198,12 @@ mat3 getTangentSpace(vec3 normal)
 
 vec3 sampleHemisphere(vec3 normal)
 {
-    float cosTheta = random(normal.xy);
+    vec4 noise = sampleNoise();
+
+    float cosTheta = random(normalize(normal.xy+noise.xy));
     float sinTheta = sqrt(max(0.0,1.0-cosTheta*cosTheta));
 
-    float phi = 2.0*PI*random(normal.yx);
+    float phi = 2.0*PI*random(normalize(normal.yz+noise.xw));
     vec3 tangentSpaceDir = vec3(cos(phi)*sinTheta, sin(phi)*sinTheta, cosTheta);
 
     // convert direction from tangent space to world space
@@ -213,13 +240,10 @@ void main()
     // get index in global work group ie xy position
     ivec2 pixel_coords = ivec2(gl_GlobalInvocationID.xy);
 
-    ivec2 dims = imageSize(img_output);                                         // fetch image dimensions
-    vec2 uv;
-    uv.x = (float(pixel_coords.x * 2 - dims.x) / dims.x) * dims.x/dims.y;       // account for aspect ratio
-    uv.y = (float(pixel_coords.y * 2 - dims.y) / dims.y);
+    vec2 uv = pixelUv();
 
     int samples = 2;
-    int bounces = 3;
+    int bounces = 2;
 
     for (int i = 0; i < samples; i++) 
     {
@@ -244,6 +268,8 @@ void main()
     //pixel = vec4(hit.albedo,1.0);
     //pixel *= (1.0-depth);
 
+    //pixel = texture(_noise, uv);
+
     // output to a specific pixel in the image
     imageStore(img_output, pixel_coords, pixel);
 }

src/gfx.c

@@ -1,4 +1,5 @@
 #include "gfx.h"
+#include "random.h"
 #include "stb_image.h"
 
 float vertices[] = {
@@ -58,6 +59,10 @@ SDL_Window* gfxInit(int width, int height)
     glGetIntegerv(GL_MAX_UNIFORM_LOCATIONS, &uniformLocations);
     printf("max uniform locations %d\n", uniformLocations);
 
+    int imageUnits;
+    glGetIntegerv(GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS, &imageUnits);
+    printf("max texture image units %d\n", imageUnits);
+
     return sdlWindow;
 }
 
@@ -191,6 +196,38 @@ void createTextureFromFile(const char* imagePath)
     stbi_image_free(data);
 }
 
+// creates a noise texture in active texture 1
+GLuint createNoiseTexture(int width, int height)
+{
+    // same init steps as with a regular texture
+    GLuint texture;
+    glGenTextures(1, &texture);
+    glActiveTexture(GL_TEXTURE1);
+    glBindTexture(GL_TEXTURE_2D, texture);
+
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_REPEAT);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_REPEAT);
+
+    int channels = 4; // rgba
+    int length = width*height*channels;
+    printf("generating %d random floats\n", length);
+
+    float data[width*height*channels];
+
+    for (int i = 0; i < length; i++)
+    {
+        data[i] = randomFloat();
+    }
+
+    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA32F, width, height, 0, GL_RGBA, GL_FLOAT, data);
+    glBindImageTexture(0, texture, 0, GL_FALSE, 0, GL_READ_ONLY, GL_RGBA32F);
+    glGenerateMipmap(GL_TEXTURE_2D);
+
+    return texture;
+}
+
 GLuint createWriteOnlyTexture(int width, int height)
 {
     GLuint texture;

src/gfx.h

@@ -7,12 +7,14 @@
 #include <SDL2/SDL_opengl.h>
 
 #include "io.h"
+#include "random.h"
 
 SDL_Window* gfxInit(int width, int height);
 
 unsigned int compileQuadShaderProgram(const char* vsPath, const char* fsPath);
 unsigned int compileComputeShaderProgram();
 
+GLuint createNoiseTexture(int width, int height);
 void createTextureFromFile(const char* path);
 GLuint createWriteOnlyTexture(int width, int height);
 void printWorkGroupLimits();

src/main.c

@@ -13,9 +13,14 @@ void updateUniforms(GLuint shaderProgram);
 
 int main()
 {
+    randomInit();
+
     // create a window and opengl context
     SDL_Window* window = gfxInit(WIDTH, HEIGHT);
 
+    // generate noise
+    GLuint noise = createNoiseTexture(WIDTH, HEIGHT);
+
     // create a texture for the compute shader to write to
     GLuint textureOutput = createWriteOnlyTexture(WIDTH, HEIGHT);
     printWorkGroupLimits();
@@ -27,18 +32,21 @@ int main()
             "bin/shader.vert", 
             "bin/shader.frag");
 
+    glBindTexture(GL_TEXTURE_2D, noise);
+    int noiseLoc = glGetUniformLocation(computeProgram, "_noise");
+    glUniform1i(noiseLoc, noise);
+
     // initialise quad
     initBuffers();
     setVertexAttributes();
 
+    int frames = 0;
     // render loop
     while (!checkQuit())
     {
-        glUseProgram(computeProgram);
-
-        updateUniforms(computeProgram);
-
         // dispatch compute shader
+        glUseProgram(computeProgram);
+        updateUniforms(computeProgram);
         glDispatchCompute((GLuint)WIDTH, (GLuint)HEIGHT, 1);
 
         // make sure we're finished writing to the texture before trying to read it
@@ -46,15 +54,23 @@ int main()
 
         // normal drawing pass
         glUseProgram(quadProgram);
-        glActiveTexture(GL_TEXTURE0);                                           // use computed texture
-        glBindTexture(GL_TEXTURE_2D, textureOutput);
 
+        // bind texture written to by compute stage to 2d target
+        glBindTexture(GL_TEXTURE_2D, textureOutput);
         glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
 
         // swip swap
         SDL_GL_SwapWindow(window);
+
+        frames++;
     }
 
+    float elapsed = now();
+    printf("%d frames in %f seconds (avg: %f fps)\n", 
+            frames, 
+            elapsed, 
+            (float)frames/elapsed);
+
     return 0;
 }