screenspace uv

main.c

@@ -2,77 +2,8 @@
 
 #include <stdio.h>
 #include <GL/gl.h>
-#include <GL/glext.h>
 #include <SDL3/SDL.h>
 
-float tanf(float in) {
-    return in;
-}
-
-void perspective(float fovY, float aspect, float zNear, float zFar, float* matrix) {
-    float f = 1.0f / tanf(fovY * 0.5f * (3.14159265358979323846f / 180.0f));
-    matrix[0]  = f / aspect;
-    matrix[1]  = 0;
-    matrix[2]  = 0;
-    matrix[3]  = 0;
-
-    matrix[4]  = 0;
-    matrix[5]  = f;
-    matrix[6]  = 0;
-    matrix[7]  = 0;
-
-    matrix[8]  = 0;
-    matrix[9]  = 0;
-    matrix[10] = (zFar + zNear) / (zNear - zFar);
-    matrix[11] = -1;
-
-    matrix[12] = 0;
-    matrix[13] = 0;
-    matrix[14] = (2 * zFar * zNear) / (zNear - zFar);
-    matrix[15] = 0;
-}
-
-void drawCube() {
-    glBegin(GL_QUADS);
-
-    // Back
-    glColor3f(0, 1, 0);
-    glVertex3f(-1, -1, -1);
-    glVertex3f(-1,  1, -1);
-    glVertex3f( 1,  1, -1);
-    glVertex3f( 1, -1, -1);
-
-    // Top
-    glColor3f(0, 0, 1);
-    glVertex3f(-1, 1, -1);
-    glVertex3f(-1, 1,  1);
-    glVertex3f( 1, 1,  1);
-    glVertex3f( 1, 1, -1);
-
-    // Bottom
-    glColor3f(1, 1, 0);
-    glVertex3f(-1, -1, -1);
-    glVertex3f( 1, -1, -1);
-    glVertex3f( 1, -1,  1);
-    glVertex3f(-1, -1,  1);
-
-    // Right
-    glColor3f(1, 0, 1);
-    glVertex3f(1, -1, -1);
-    glVertex3f(1,  1, -1);
-    glVertex3f(1,  1,  1);
-    glVertex3f(1, -1,  1);
-
-    // Left
-    glColor3f(0, 1, 1);
-    glVertex3f(-1, -1, -1);
-    glVertex3f(-1, -1,  1);
-    glVertex3f(-1,  1,  1);
-    glVertex3f(-1,  1, -1);
-
-    glEnd();
-}
-
 void checkGlError() {
     const char *err = SDL_GetError();
     if (*err != 0) {
@@ -80,13 +11,47 @@ void checkGlError() {
     }
 }
 
-const char *vertex_shader_source = "";
+const char *fragment_shader_source =
+"#version 330 core\n"
+"out vec4 FragColor;\n"
+"in vec2 uv;\n"
+"\n"
+"void main()\n"
+"{\n"
+"    FragColor = vec4(gl_FragCoord.xy / 800, 0.0, 1.0);\n"
+"}\n";
 
-GLuint create_shader() {
+GLuint compile_shader(GLuint type, const char *src) {
-    GLuint vshader = glCreateShader(GL_VERTEX_SHADER);
+    GLuint id = glCreateShader(GL_FRAGMENT_SHADER);
-    glShaderSource(vshader, 1, &vertex_shader_source, NULL); // vertex_shader_source is a GLchar* containing glsl shader source code
+    glShaderSource(id, 1, &src, 0);
-    glCompileShader(vshader);
+    glCompileShader(id);
-    return vshader;
+
+    int result;
+    glGetShaderiv(id, GL_COMPILE_STATUS, &result);
+    if (result == GL_FALSE) {
+        int length;
+        glGetShaderiv(id, GL_INFO_LOG_LENGTH, &result);
+        char *message = alloca(length * sizeof(char));
+        glGetShaderInfoLog(id, length, &length, message);
+        printf("failed to compile %s shader\n", type == GL_VERTEX_SHADER ? "vertex" : "fragment");
+        printf("%s\n", message);
+        glDeleteShader(id);
+        return 0;
+    }
+
+    return id;
+}
+
+GLuint create_shader(const char *fragment_src) {
+    GLuint program = glCreateProgram();
+    GLuint fragment_shader = compile_shader(GL_FRAGMENT_SHADER, fragment_src);
+
+    glAttachShader(program, fragment_shader);
+    glLinkProgram(program);
+    glValidateProgram(program);
+    glDeleteShader(fragment_shader);
+
+    return program;
 }
 
 int main() {
@@ -112,6 +77,10 @@ int main() {
     SDL_Event e;
     int running = 1;
     float angle = 0.0;
+
+    GLuint shader = create_shader(fragment_shader_source);
+    glUseProgram(shader);
+
     while (running) {
         while (SDL_PollEvent(&e)) {
             if (e.type == SDL_EVENT_QUIT) running = false;
@@ -119,18 +88,18 @@ int main() {
         checkGlError();
 
         // Rendorrrr
-        glViewport(0, 0, 800, 600);
+        glViewport(0, 0, 800, 800);
         glClearColor(0.1f, 0.1f, 0.1f, 1.0f);  // Dark gray background
         glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
         
         //drawCube();
         // Front
         glBegin(GL_QUADS);
-        glColor3f(1, 0, 0);
-        glVertex2f(-1, -1);
         glVertex2f(-1, 1);
+        glVertex2f(-1,-1);
+        glVertex2f( 1,-1);
         glVertex2f( 1, 1);
-        glVertex2f( 1, -1);
+
         glEnd();
 
         SDL_GL_SwapWindow(window);