rotations; depth shade

CMakeLists.txt

@@ -1,5 +1,5 @@
 cmake_minimum_required(VERSION 3.10)
-project(main)
+project(hopf)
 
 set(CMAKE_CXX_STANDARD 17)
 

main/shaders/main.frag

@@ -1,7 +1,17 @@
 #version 440
 
+#define PI 3.14159
+
+in vec4 pos;
+in vec4 pos4;
+in vec4 pos3;
+
 out vec4 color;
 
 void main() {
-    color = vec4(1);
+    float light = -pos3.y / 10 + .5;
+
+    vec3 col = vec3(1);
+
+    color = vec4(col * light, 1);
 }

main/shaders/main.geom

@@ -1,31 +1,47 @@
 #version 440
 
-#define CIRCLE_RES 256
+#define CIRCLE_RES 64
 #define PI 3.14159
 
 layout(points) in;
 layout(line_strip, max_vertices=CIRCLE_RES) out;
 
+layout(binding=1) uniform Matrices {
+    mat4 proj;
+    mat4 model;
+};
+
 in float xi_[];
 in float eta_[];
 
-layout(binding=1) uniform Matrices {
-    mat4 proj;
-};
+out vec4 pos;
+out vec4 pos4;
+out vec4 pos3;
 
 void main(){
     for(int k = 0; k <= CIRCLE_RES; k++) {
-        vec2 xi = vec2(xi_[0], 4 * PI * k / CIRCLE_RES);
+        vec2 xi = vec2(xi_[0], 4 * PI * k / (CIRCLE_RES - 1));
         float eta = eta_[0];
 
+        // todo parameterize the projected circle so there aren't jagged edges.
+        // should be smooth at <=32 segments, not just 128+
         float x = cos((xi.y + xi.x) / 2) * sin(eta);
         float y = sin((xi.y + xi.x) / 2) * sin(eta);
         float z = cos((xi.y - xi.x) / 2) * cos(eta);
         float w = sin((xi.y - xi.x) / 2) * cos(eta);
 
-        vec4 pos = vec4(x / (1 - w), y / (1 - w), z / (1 - w), 1);
+        pos = vec4(x, y, z, w);
+        pos4 = model * pos;
+        pos3 = vec4(pos4.xyz / (1 - pos4.w), 1);
+        gl_Position = proj * pos3;
+
+        if (length(gl_Position) > 4) {
+            EndPrimitive();
+            continue;
+        }
 
-        gl_Position = proj * pos;
         EmitVertex();
     }
+
+    EndPrimitive();
 }

main/src/main.cpp

@@ -5,6 +5,7 @@
 #include <fstream>
 #include <sstream>
 #include <vector>
+#include <cmath>
 
 #define PI 3.14159f
 
@@ -107,8 +108,12 @@ namespace util {
 }
 
 struct HopfCircle {
-    float xi;
-    float eta;
+    float xi; // longitude
+    float eta; // latitude
+
+    HopfCircle(float xi, float eta) : xi(xi), eta(eta) {}
+
+    HopfCircle() : HopfCircle(0, 0) {}
 };
 
 struct State {
@@ -120,30 +125,36 @@ struct State {
 
     std::vector<HopfCircle> circles{};
 
-    explicit State(GLFWwindow *window) {
+    float t = 0;
+
+    void regen() {
+        circles.clear();
+
         const int N = 32;
-        for (int k = 0; k < N; ++k) {
-            circles.push_back({2 * PI * k / N, 0.025});
-            circles.push_back({2 * PI * k / N, PI / 2 - 0.025});
+        const int M = 4;
+        const float PAD = 0.0125;
 
-            circles.push_back({2 * PI * k / N, 0.3f});
-            circles.push_back({2 * PI * k / N, 0.4f});
-            circles.push_back({2 * PI * k / N, 0.5f});
-
-            circles.push_back({2 * PI * k / N, 1.1f});
-            circles.push_back({2 * PI * k / N, 1.2f});
-            circles.push_back({2 * PI * k / N, 1.3f});
+        for (int k = 0; k <= N; ++k) {
+            for (int j = 0; j <= M; ++j) {
+                float xi = 2 * PI * k / N;
+                float eta = (PI / 2 - 2 * PAD) * j / M + PAD;
+                circles.emplace_back(xi, eta);
+            }
         }
 
+        glBindBuffer(GL_ARRAY_BUFFER, vbo);
+        util::bufferData(GL_ARRAY_BUFFER, circles, GL_STREAM_DRAW);
+        glBindBuffer(GL_ARRAY_BUFFER, 0);
+    }
+
+    explicit State(GLFWwindow *window) {
         printf("vendor: %s\nrenderer: %s\n", glGetString(GL_VENDOR), glGetString(GL_RENDERER));
 
         glGenBuffers(1, &vbo);
         glGenBuffers(1, &ubo);
         glGenVertexArrays(1, &vao);
 
-        glBindBuffer(GL_ARRAY_BUFFER, vbo);
-        util::bufferData<HopfCircle>(GL_ARRAY_BUFFER, circles, GL_STATIC_DRAW);
-        glBindBuffer(GL_ARRAY_BUFFER, 0);
+        regen();
 
         glBindBufferBase(GL_UNIFORM_BUFFER, ubo_bp, ubo);
 
@@ -180,12 +191,25 @@ struct State {
         glfwGetFramebufferSize(window, &w, &h);
         auto ar = (float) w / h;
 
+        t += dt;
+
+        float c = std::cos(t / 8);
+        float s = std::sin(t / 8);
+
+        float c_ = std::cos(3.f / 8);
+        float s_ = std::sin(3.f / 8);
+
         glBindBuffer(GL_UNIFORM_BUFFER, ubo);
         util::bufferData<float>(GL_UNIFORM_BUFFER, {
             1.f / 4 / ar, 0, 0, 0,
             0, 0, 1.f / 10, 0,
             0, 1.f / 4, 0, 0,
-            0, 0, 0, 1
+            0, 0, 0, 1,
+
+            c, 0, 0, s,
+            0, c_, s_, 0,
+            0, -s_, c_, 0,
+            -s, 0, 0, c
         }, GL_STREAM_DRAW);
         glBindBuffer(GL_UNIFORM_BUFFER, 0);
     }
@@ -195,12 +219,13 @@ struct State {
         glfwGetFramebufferSize(window, &w, &h);
         glViewport(0, 0, w, h);
 
-        glClear(GL_COLOR_BUFFER_BIT);
+        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 
         glUseProgram(prog);
         glBindVertexArray(vao);
+        glEnable(GL_DEPTH_TEST);
         glPointSize(5);
-        glLineWidth(3);
+        glLineWidth(5);
         glDrawArrays(GL_POINTS, 0, (unsigned) circles.size());
         glBindVertexArray(0);
         glUseProgram(0);