Add demo for Hierarchical Sample Warping

README.md

@@ -23,6 +23,10 @@ Demo suite for LWJGL 3
 
 ![opengl/raytracing/tutorial/Tutorial8_2.java](md/tutorial8_2.jpg)
 
+[opengl/sampling/HierarchicalSampleWarping.java](./src/org/lwjgl/demo/opengl/sampling/HierarchicalSampleWarping.java)
+
+![opengl/sampling/HierarchicalSampleWarping.java](md/hsw.jpg)
+
 ## Building
 
     ./mvnw package

res/org/lwjgl/demo/opengl/sampling/hsw.fs.glsl

@@ -0,0 +1,65 @@
+/*
+ * Copyright LWJGL. All rights reserved.
+ * License terms: https://www.lwjgl.org/license
+ */
+#version 330 core
+
+uniform sampler2D tex;
+uniform float time;
+uniform float blendFactor;
+
+in vec2 texcoords;
+out vec4 color;
+
+uvec3 pcg3d(uvec3 v) {
+  v = v * 1664525u + 1013904223u;
+  v.x += v.y * v.z;
+  v.y += v.z * v.x;
+  v.z += v.x * v.y;
+  v ^= v >> 16u;
+  v.x += v.y * v.z;
+  v.y += v.z * v.x;
+  v.z += v.x * v.y;
+  return v;
+}
+vec3 random3(vec3 f) {
+  return uintBitsToFloat((pcg3d(floatBitsToUint(f)) & 0x007FFFFFu) | 0x3F800000u) - vec3(1.0);
+}
+float luminance(vec3 rgb) {
+  return dot(rgb, vec3(0.2126, 0.7152, 0.0722));
+}
+vec2 importanceSampleHierarchicalWarping(sampler2D t, vec2 u) {
+  int x = 0, y = 0;
+  vec2 u0 = u;
+  ivec2 texSize = textureSize(t, 0);
+  int maxLod = int(log2(float(texSize.x)) - 0.5);
+  for (int lod = maxLod; lod >= 0; lod--) {
+    x <<= 1; y <<= 1;
+    float x0y0 = luminance(texelFetch(t, ivec2(x+0,y+0), lod).rgb);
+    float x1y0 = luminance(texelFetch(t, ivec2(x+1,y+0), lod).rgb);
+    float x0y1 = luminance(texelFetch(t, ivec2(x+0,y+1), lod).rgb);
+    float x1y1 = luminance(texelFetch(t, ivec2(x+1,y+1), lod).rgb);
+    float left = x0y0 + x0y1, right = x1y0 + x1y1, pLeft = left / (left + right);
+    float uxFactor = step(pLeft, u.x);
+    float pLower = mix(x0y0 / left, x1y0 / right, uxFactor);
+    float uyFactor = step(pLower, u.y);
+    float uxDen = mix(pLeft, 1.0 - pLeft, uxFactor), uyDen = mix(pLower, 1.0 - pLower, uyFactor);
+    u.x = mix(u.x, u.x - pLeft, uxFactor) / uxDen; u.y = mix(u.y, u.y - pLower, uyFactor) / uyDen;
+    x += int(uxFactor); y += int(uyFactor);
+  }
+  return (vec2(x, y) + u0) / vec2(texSize);
+}
+float distMetric(vec2 a, vec2 b) {
+  return sqrt(dot(a - b, a - b));
+}
+void main(void) {
+  vec3 c = texture(tex, texcoords).rgb;
+  vec3 rnd = random3(vec3(texcoords, time));
+  vec2 s = importanceSampleHierarchicalWarping(tex, rnd.xy);
+  float dist = distMetric(texcoords, s);
+  float distanceRandomness = 0.01 + rnd.z * 0.05;
+  if (dist < distanceRandomness)
+    c = vec3(15.0, 0.0, 0.0);
+  //color = vec4(c, blendFactor);
+  color = vec4(c, 0.5);
+}

res/org/lwjgl/demo/opengl/sampling/hsw.vs.glsl

@@ -0,0 +1,13 @@
+/*
+ * Copyright LWJGL. All rights reserved.
+ * License terms: https://www.lwjgl.org/license
+ */
+#version 330 core
+out vec2 texcoords;
+void main(void) {
+  vec2 vertex = vec2(-1.0) + vec2(
+    float((gl_VertexID & 1) << 2),
+    float((gl_VertexID & 2) << 1));
+  texcoords = vertex * 0.5 + 0.5;
+  gl_Position = vec4(vertex, 0.0, 1.0);
+}

src/org/lwjgl/demo/opengl/sampling/HierarchicalSampleWarping.java

@@ -0,0 +1,169 @@
+package org.lwjgl.demo.opengl.sampling;
+
+import org.lwjgl.BufferUtils;
+import org.lwjgl.demo.opengl.util.DemoUtils;
+import org.lwjgl.glfw.GLFWKeyCallback;
+import org.lwjgl.opengl.GL;
+import org.lwjgl.system.MemoryStack;
+
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.nio.FloatBuffer;
+import java.nio.IntBuffer;
+
+import static org.lwjgl.demo.util.IOUtils.ioResourceToByteBuffer;
+import static org.lwjgl.glfw.GLFW.*;
+import static org.lwjgl.opengl.GL33C.*;
+import static org.lwjgl.stb.STBImage.*;
+import static org.lwjgl.system.MemoryStack.stackPush;
+import static org.lwjgl.system.MemoryUtil.NULL;
+import static org.lwjgl.system.MemoryUtil.memAddress;
+
+/**
+ * Demo showcasing Hierarchical Sample Warping (HSW) as first proposed in the paper
+ * "Wavelet Importance: Efficiently Evaluating Products of Complex Functions" by Clarberg et al.
+ * <p>
+ * This demo implements importance sampling via hierarchical sample warping in its associated fragment shader
+ * by using a 2D lightmap texture and generating samples with probabilities proportional to a texel's luminance.
+ * <p>
+ * See:
+ * <ul>
+ * <li><a href="https://link.springer.com/content/pdf/10.1007/978-1-4842-4427-2_16.pdf">section 16.4.2.3 HIERARCHICAL TRANSFORMATION in chapter "Transformations Zoo" of "Ray Tracing Gems".</a></li>
+ * <li><a href="http://graphics.ucsd.edu/~henrik/papers/wavelet_importance_sampling.pdf">"Wavelet Importance: Efficiently Evaluating Products of Complex Functions" by Clarberg et al.</a></li>
+ * <li><a href="https://www.ea.com/seed/news/siggraph21-global-illumination-surfels">SIGGRAPH 21: Global Illumination Based on Surfels</a></li>
+ * </ul>
+ *
+ * @author Kai Burjack
+ */
+public class HierarchicalSampleWarping {
+  private static int width = 800, height = 800;
+  public static void main(String[] args) throws IOException {
+    if (!glfwInit())
+      throw new IllegalStateException("Unable to initialize GLFW");
+    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
+    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
+    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
+    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GLFW_TRUE);
+    glfwWindowHint(GLFW_VISIBLE, GLFW_FALSE);
+    glfwWindowHint(GLFW_RESIZABLE, GLFW_FALSE);
+    long window = glfwCreateWindow(width, height, "Hello HSW!", NULL, NULL);
+    if (window == NULL)
+      throw new RuntimeException("Failed to create the GLFW window");
+    glfwSetKeyCallback(window, new GLFWKeyCallback() {
+      public void invoke(long window, int key, int scancode, int action, int mods) {
+        if (action != GLFW_RELEASE)
+          return;
+        if (key == GLFW_KEY_ESCAPE)
+          glfwSetWindowShouldClose(window, true);
+      }
+    });
+    glfwMakeContextCurrent(window);
+    glfwSwapInterval(1);
+    GL.createCapabilities();
+
+    // Read actualy framebuffer size for HiDPI displays
+    try (MemoryStack stack = stackPush()) {
+      IntBuffer framebufferSize = stack.mallocInt(2);
+      nglfwGetFramebufferSize(window, memAddress(framebufferSize), memAddress(framebufferSize) + 4);
+      width = framebufferSize.get(0);
+      height = framebufferSize.get(1);
+    }
+
+    // Create shader program which implements visualization of the hierarchical sample warping
+    int program = glCreateProgram();
+    {
+      int vshader = DemoUtils.createShader("org/lwjgl/demo/opengl/sampling/hsw.vs.glsl", GL_VERTEX_SHADER, null);
+      int fshader = DemoUtils.createShader("org/lwjgl/demo/opengl/sampling/hsw.fs.glsl", GL_FRAGMENT_SHADER, null);
+      glAttachShader(program, vshader);
+      glAttachShader(program, fshader);
+      glBindFragDataLocation(program, 0, "color");
+      glLinkProgram(program);
+      int linked = glGetProgrami(program, GL_LINK_STATUS);
+      String programLog = glGetProgramInfoLog(program);
+      if (programLog.trim().length() > 0)
+        System.err.println(programLog);
+      if (linked == 0)
+        throw new AssertionError("Could not link program");
+    }
+    glUseProgram(program);
+    glUniform1i(glGetUniformLocation(program, "tex"), 0);
+    int timeLocation = glGetUniformLocation(program, "time");
+    int blendFactorLocation = glGetUniformLocation(program, "blendFactor");
+
+    // Create empty VAO
+    int vao = glGenVertexArrays();
+    glBindVertexArray(vao);
+
+    // Create FBO with 32-bit floating point color buffer to do the sample accumulation
+    int fbo = glGenFramebuffers();
+    glBindFramebuffer(GL_FRAMEBUFFER, fbo);
+    int framebufferTex = glGenTextures();
+    {
+      glBindTexture(GL_TEXTURE_2D, framebufferTex);
+      glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA32F, width, height, 0, GL_RGBA, GL_FLOAT, (ByteBuffer) null);
+      glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+      glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+      glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, framebufferTex, 0);
+      if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
+        throw new AssertionError("Incomplete framebuffer");
+    }
+
+    // Load an image, that we want to sample via hierarchical sample warping, into a texture
+    // and generate mipmaps for it
+    int tex = glGenTextures();
+    {
+      glBindTexture(GL_TEXTURE_2D, tex);
+      glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
+      glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
+      glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
+      glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
+      IntBuffer w = BufferUtils.createIntBuffer(1);
+      IntBuffer h = BufferUtils.createIntBuffer(1);
+      IntBuffer comp = BufferUtils.createIntBuffer(1);
+      ByteBuffer imageBuffer = ioResourceToByteBuffer("org/lwjgl/demo/opengl/sampling/env-square2.hdr", 64 * 1024);
+      stbi_set_flip_vertically_on_load(true);
+      if (!stbi_info_from_memory(imageBuffer, w, h, comp))
+        throw new IOException("Failed to read image information: " + stbi_failure_reason());
+      FloatBuffer image = stbi_loadf_from_memory(imageBuffer, w, h, comp, 3);
+      if (image == null)
+        throw new IOException("Failed to load image: " + stbi_failure_reason());
+      glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB32F, w.get(0), h.get(0), 0, GL_RGB, GL_FLOAT, (ByteBuffer) null);
+      glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, w.get(0), h.get(0), GL_RGB, GL_FLOAT, image);
+      stbi_image_free(image);
+      glGenerateMipmap(GL_TEXTURE_2D);
+    }
+
+    glfwShowWindow(window);
+
+    long lastTime = System.nanoTime();
+    float time = 0.0f;
+    int frameNumber = 0;
+
+    // Enable blending for sample accumulation in the FBO
+    glBlendFunc(GL_ONE_MINUS_SRC_ALPHA, GL_SRC_ALPHA);
+    glEnable(GL_BLEND);
+
+    while (!glfwWindowShouldClose(window)) {
+      glfwPollEvents();
+
+      long thisTime = System.nanoTime();
+      float elapsed = (thisTime - lastTime) / 1E9f;
+      time += elapsed;
+      lastTime = thisTime;
+
+      glViewport(0, 0, width, height);
+      glBindFramebuffer(GL_DRAW_FRAMEBUFFER, fbo);
+      glUseProgram(program);
+      glBindTexture(GL_TEXTURE_2D, tex);
+      glUniform1f(blendFactorLocation, frameNumber / (frameNumber + 1.0f));
+      glUniform1f(timeLocation, time);
+      glDrawArrays(GL_TRIANGLES, 0, 3);
+      glBindFramebuffer(GL_READ_FRAMEBUFFER, fbo);
+      glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
+      glBlitFramebuffer(0, 0, width, height, 0, 0, width, height, GL_COLOR_BUFFER_BIT, GL_NEAREST);
+
+      glfwSwapBuffers(window);
+      frameNumber++;
+    }
+  }
+}