1. rcrnstn/sdf-winding
  2. Commit a539a745a49339fb415d5d6d2bf0befe47dfe841
Browse code

Add OpenGL boilerplate

Robert Cranston authored on 08/03/2026 00:46:06
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.gitignore
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+/sdf-winding
Makefile
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+CXXFLAGS += -std=c++11
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+CXXFLAGS += -Wall -Wextra -Wpedantic
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+CXXFLAGS += -Wconversion -Wsign-conversion
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+CXXFLAGS += -Wshadow
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+CXXFLAGS += -Og -g -fsanitize=undefined,address
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+LDLIBS   += -lGL -lGLEW -lglfw
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+
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+sdf-winding:
README.md
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 I have not read a single word of that reference manual, proceed accordingly.
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+To build, run `make`. You need the following dependencies on your system:
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+
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+-   OpenGL
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+-   [GLEW][]
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+-   [GLFW][]
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+
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 [`sdf-winding`]:  https://git.rcrnstn.net/rcrnstn/sdf-winding
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 [glyph]:          https://en.wikipedia.org/wiki/Glyph
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 [winding number]: https://en.wikipedia.org/wiki/Winding_number
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 [SDF]:            https://en.wikipedia.org/wiki/Signed_distance_function
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 [Figure 7]:       https://developer.apple.com/fonts/TrueType-Reference-Manual/RM02/FE6.gif
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 [TrueType]:       https://developer.apple.com/fonts/TrueType-Reference-Manual/RM02/Chap2.html#distinguishing
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+[GLEW]:           https://glew.sourceforge.net
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+[GLFW]:           https://www.glfw.org
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 ## License
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sdf-winding.cpp
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+/// Includes
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+
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+#include <ctime>
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+#include <sstream>
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+#include <fstream>
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+#include <iostream>
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+#include <iomanip>
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+
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+#include <GL/glew.h>
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+#include <GLFW/glfw3.h>
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+
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+/// Constants
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+
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+constexpr auto width  = 640;
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+constexpr auto height = 480;
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+constexpr auto title  = "";
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+
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+/// Helpers
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+
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+//// Debug
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+void GLAPIENTRY debug_message_callback(
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+    GLenum          /* source   */,
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+    GLenum          /* type     */,
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+    GLuint          /* id       */,
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+    GLenum          /* severity */,
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+    GLsizei         /* length   */,
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+    GLchar  const *    message,
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+    void    const * /* param    */
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+)
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+{
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+    std::cerr << message << std::endl;
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+};
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+
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+//// Uniform
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+void uniform(GLint location, int            value    ) { glUniform1i (location,    value); }
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+void uniform(GLint location, bool           value    ) { glUniform1i (location,    value); }
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+void uniform(GLint location, float          value    ) { glUniform1f (location,    value); }
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+void uniform(GLint location, float const (& value)[1]) { glUniform1fv(location, 1, value); }
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+void uniform(GLint location, float const (& value)[2]) { glUniform2fv(location, 1, value); }
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+void uniform(GLint location, float const (& value)[3]) { glUniform3fv(location, 1, value); }
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+void uniform(GLint location, float const (& value)[4]) { glUniform4fv(location, 1, value); }
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+template<typename T>
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+void uniform(char const * name, T const & value)
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+{
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+    GLuint program;   glGetIntegerv(GL_CURRENT_PROGRAM, (GLint *)&program);
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+    GLint  location = glGetUniformLocation(program, name);
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+    uniform(location, value);
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+}
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+
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+//// Write
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+void write_tga(char const * base)
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+{
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+    char header[] = {
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+        0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0,
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+        (char)(width  >> 0U),
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+        (char)(width  >> 8U),
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+        (char)(height >> 0U),
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+        (char)(height >> 8U),
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+        4*8, 0,
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+    };
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+    char data[4*width*height];
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+    glPixelStorei(GL_PACK_ALIGNMENT, 1);
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+    glReadPixels(0, 0, width, height, GL_BGRA, GL_UNSIGNED_BYTE, data);
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+    auto t  = std::time(nullptr);
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+    auto pt = std::put_time(std::localtime(&t), "%Y-%m-%d_%H-%M-%S");
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+    std::ofstream((std::ostringstream{} << base << "_" << pt << ".tga").str())
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+        .write(header, sizeof(header))
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+        .write(data,   sizeof(data));
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+}
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+
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+/// Main
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+
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+int main(int /*argc*/, char * argv[])
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+{
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+    //// Window/context
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+    glfwInit();
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+    auto window = glfwCreateWindow(width, height, title, nullptr, nullptr);
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+    glfwMakeContextCurrent(window);
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+    glewInit();
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+
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+    //// Callbacks
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+    glfwSetWindowUserPointer(window, argv[0]);
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+    glfwSetKeyCallback(window,
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+        [](GLFWwindow* w, int key, int /*scancode*/, int action, int /*mods*/)
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+        {
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+            auto ptr = glfwGetWindowUserPointer(w);
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+            if (action != GLFW_RELEASE) return;
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+            if (key == GLFW_KEY_Q) glfwSetWindowShouldClose(w, GLFW_TRUE);
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+            if (key == GLFW_KEY_W) write_tga((char *)ptr);
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+        }
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+    );
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+
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+    //// Debug
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+    glEnable(GL_DEBUG_OUTPUT);
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+    glEnable(GL_DEBUG_OUTPUT_SYNCHRONOUS);
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+    glDebugMessageCallback(debug_message_callback, nullptr);
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+
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+    //// Shader
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+    auto make_program = [](char const * vert_source, char const * frag_source)
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+    {
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+        auto program = glCreateProgram();
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+        auto vert    = glCreateShader(GL_VERTEX_SHADER);
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+        auto frag    = glCreateShader(GL_FRAGMENT_SHADER);
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+        glShaderSource(vert, 1, &vert_source, nullptr);
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+        glShaderSource(frag, 1, &frag_source, nullptr);
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+        glCompileShader(vert);
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+        glCompileShader(frag);
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+        glAttachShader(program, vert);
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+        glAttachShader(program, frag);
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+        glLinkProgram(program);
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+        return program;
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+    };
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+    auto vert_source = R"(
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+        #version 140
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+
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+        out vec2 tex_coord;
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+
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+        void main()
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+        {
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+            tex_coord = vec2[](
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+                vec2(0, 0),
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+                vec2(2, 0),
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+                vec2(0, 2)
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+            )[gl_VertexID];
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+            gl_Position = vec4(tex_coord*2-1, 0, 1);
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+        }
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+    )";
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+    auto tex_coord_program = make_program(vert_source, R"(
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+        #version 140
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+
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+        uniform int   view;
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+        uniform bool  debug;
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+        uniform float time;
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+
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+        in vec2 tex_coord;
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+
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+        void main()
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+        {
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+            gl_FragColor = vec4(fract(tex_coord - float(!debug)*time), 0, 1);
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+
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+            // Exercise the debugging colors.
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+            // <https://www.desmos.com/calculator/uijwefecqs>
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+            if (view >= 2)
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+            {
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+                float x = tex_coord.x;
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+                x -= 0.5;
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+                x *= 10;
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+                x  = clamp(x, -3, +3);
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+                x /= (3 + x) * (3 - x);
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+                x *= (3 + 1) * (3 - 1);
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+                x *= 0.5;
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+                x += 0.5;
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+                gl_FragColor = vec4(x / (1 / float(tex_coord.y > 0.5)));
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+            }
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+
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+            bvec3 debug_color = bvec3(
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+                any(lessThan   (gl_FragColor, vec4(0))),
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+                any(greaterThan(gl_FragColor, vec4(1))),
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+                any(isinf      (gl_FragColor)) ||
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+                any(isnan      (gl_FragColor))
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+            );
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+            if (debug && any(debug_color))
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+                gl_FragColor = vec4(debug_color, 1);
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+        }
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+    )");
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+
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+    //// Main loop
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+    int   view  = 1;
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+    bool  debug = true;
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+    float time  = (float)glfwGetTime();
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+    while (glfwPollEvents(), !glfwWindowShouldClose(window))
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+    {
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+        ///// Time
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+        float pt = time;
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+        float dt = (time = (float)glfwGetTime()) - pt;
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+
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+        ///// Input
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+        for (int num = 0; num <= 9; ++num)
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+        if (glfwGetKey(window, GLFW_KEY_0 + num)) view  = num;
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+        if (glfwGetKey(window, GLFW_KEY_R))       debug = false;
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+        if (glfwGetKey(window, GLFW_KEY_E))       debug = true;
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+
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+        ///// Draw
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+        glClear(GL_COLOR_BUFFER_BIT);
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+        glUseProgram(tex_coord_program);
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+        uniform("view",  view);
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+        uniform("debug", debug);
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+        uniform("time",  time);
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+        uniform("dt",    dt);
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+        glDrawArrays(GL_TRIANGLES, 0, 3);
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+
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+        ///// Swap
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+        glfwSwapBuffers(window);
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+    }
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+
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+    //// Cleanup
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+    glfwDestroyWindow(window);
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+    glfwTerminate();
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+}