From 089458476f2b1bad381b3b6cb919280ffdcb596c Mon Sep 17 00:00:00 2001
From: ktyl <me@ktyl.dev>
Date: Wed, 1 Mar 2023 00:12:15 +0000
Subject: [PATCH] generate blue noise points

---
 src/gfx.c | 126 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
 src/gfx.h |   2 +
 2 files changed, 127 insertions(+), 1 deletion(-)

diff --git a/src/gfx.c b/src/gfx.c
index 461185b..039cbdc 100644
--- a/src/gfx.c
+++ b/src/gfx.c
@@ -197,7 +197,7 @@ int createTextures(int width, int height, struct Shaders shaders, struct Texture
 }
 
 // creates a noise texture in active texture 1
-GLuint createNoiseTexture(int width, int height)
+GLuint createWhiteNoiseTexture(int width, int height)
 {
     // same init steps as with a regular texture
     GLuint texture;
@@ -230,6 +230,130 @@ GLuint createNoiseTexture(int width, int height)
     return texture;
 }
 
+void generateBlueNoisePoints(vec2* points, int m, int n)
+{
+    vec2 firstSample = {randomFloat(), randomFloat()};
+    struct Candidate
+    {
+        vec2 pos;
+        // distance to closest point already in pattern
+        float distance;
+    };
+
+    for (int i = 0; i < n; i++)
+    {
+        // generate a bunch of candidates
+        int count = m * i;
+        struct Candidate candidates[count];
+        //int closest = -1;
+
+        for (int j = 0; j < count; j++)
+        {
+            struct Candidate* c = &candidates[j];
+
+            c->pos[0] = randomFloat();
+            c->pos[1] = randomFloat();
+            // the largest distance we should expect is sqrt(2),
+            // so pick a maximum larger than that
+            c->distance = 1.5; 
+
+            // get the distance of the closest point already in the pattern
+            for (int k = 0; k < i; k++)
+            {
+                float distance = glm_vec2_distance(c->pos, points[k]);
+                if (distance < c->distance)
+                {
+                    c->distance = distance;
+                    //closest = k;
+                }
+            }
+        }
+
+        // of our candidates, now determine which of them has the furthest
+        // closest-distance
+        int furthest = -1;
+        float furthestDistance = 0.0;
+        for (int j = 0; j < count; j++)
+        {
+            if (candidates[j].distance > furthestDistance)
+            {
+                furthest = j;
+                furthestDistance = candidates[j].distance;
+            }
+        }
+
+        glm_vec2_copy(candidates[furthest].pos, points[i]);
+    }
+}
+
+GLuint createBlueNoiseTexture(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);
+    printf("generating blue noise\n");
+
+    float* data = (float*)malloc(length*sizeof(float));
+
+    // generate a bunch of points
+    int m = 100;
+    int n = 100;
+    vec2 points[n];
+    generateBlueNoisePoints(points, m, n);
+
+    // use those points to generate a texture
+
+    //for (int i = 0; i < length; i++)
+    //{
+    //    data[i] = randomFloat();
+    //}
+
+    for (int i = 0; i < width*height; i++)
+    {
+        int pixelIdx = i;
+        int x = pixelIdx % width;
+        int y = pixelIdx / width;
+        float u = x / (float)width;
+        float v = y / (float)height;
+        vec2 pixel = {u,v};
+
+        for (int j = 0; j < n; j++)
+        {
+            float d = glm_vec2_distance(points[j], pixel);
+            float r = 0.01;
+            if (d < r)
+            {
+                data[i * channels + 2] = 1.0;
+            }
+        }
+    }
+
+    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);
+
+    free(data);
+
+    return texture;
+}
+
+GLuint createNoiseTexture(int width, int height)
+{
+    //return createWhiteNoiseTexture(width, height);
+    return createBlueNoiseTexture(width, height);
+}
+
 GLuint createWriteOnlyTexture(int width, int height)
 {
     GLuint texture;
diff --git a/src/gfx.h b/src/gfx.h
index db364e7..1c30422 100644
--- a/src/gfx.h
+++ b/src/gfx.h
@@ -6,6 +6,8 @@
 #include <SDL2/SDL.h>
 #include <SDL2/SDL_opengl.h>
 
+#include <cglm/vec2.h>
+
 #include "io.h"
 #include "random.h"