x11 window and opengl initialization and drawing of basic quad

cudoku.c

@@ -0,0 +1,44 @@
+#include <glad/gl.h>
+
+#include "shader.h"
+
+static const float quad_vertices[] = {
+  -0.5f, 1.0f, 0.0f, // top left
+   0.5f, 1.0f, 0.0f, // top right 
+  -0.5f, -1.0f, 0.0f, // bottom left
+   0.5f, -1.0f, 0.0f, // bottom right
+};
+
+static const int quad_indices[] = {
+  0, 1, 2,
+  1, 2, 3
+};
+
+unsigned int prepare_bg_rect() {
+  unsigned int vbo, vao, ebo;
+  glGenVertexArrays(1, &vao);
+  glGenBuffers(1, &vbo);
+  glGenBuffers(1, &ebo);
+
+  glBindVertexArray(vao);
+
+  glBindBuffer(GL_ARRAY_BUFFER, vbo);
+  glBufferData(GL_ARRAY_BUFFER, sizeof(quad_vertices), quad_vertices, GL_STATIC_DRAW);
+
+  glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);
+  glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(quad_indices), quad_indices, GL_STATIC_DRAW);
+
+  glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void *)0);
+  glEnableVertexAttribArray(0);
+
+  return vao;
+}
+
+void draw_bg_rect(Shader shader, unsigned int vao) {
+  use_shader(shader);
+
+  glBindVertexArray(vao);
+  glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
+
+  glBindVertexArray(0);
+}