square board and properly fit inside window

cudoku.c

@@ -3,10 +3,10 @@
 #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
+  -1.0f, 1.0f, 0.0f, // top left
+   1.0f, 1.0f, 0.0f, // top right 
+  -1.0f, -1.0f, 0.0f, // bottom left
+   1.0f, -1.0f, 0.0f, // bottom right
 };
 
 static const int quad_indices[] = {
@@ -34,9 +34,18 @@ unsigned int prepare_bg_rect() {
   return vao;
 }
 
-void draw_bg_rect(Shader shader, unsigned int vao) {
+void draw_bg_rect(Shader shader, unsigned int vao, float x_scale, float y_scale) {
   use_shader(shader);
 
+  float mat[4][4] = {
+    {x_scale, 0, 0, 0},
+    {0, y_scale, 0, 0},
+    {0, 0, 1, 0},
+    {0, 0, 0, 1},
+  };
+
+  set_mat4(shader, "transform", (float *)mat);
+
   glBindVertexArray(vao);
   glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);