simplify shader grid drawing and add option to use a texture for the grid

cudoku.c

@@ -1,13 +1,17 @@
-#include <glad/gl.h>
 #include <stdio.h>
+#include <stdbool.h>
+
+#include <glad/gl.h>
+#include "3rdparty/stb/stb_image.h"
 
 #include "shader.h"
 
 static const float quad_vertices[] = {
-  -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
+  // positions     // texture coords
+  -1.0f, 1.0f, 0.0f, 0.0f, 1.0f,  // top left
+   1.0f, 1.0f, 0.0f, 1.0f, 1.0f, // top right 
+  -1.0f, -1.0f, 0.0f, 0.0f, 0.0f, // bottom left
+   1.0f, -1.0f, 0.0f, 1.0f, 0.0f // bottom right
 };
 
 static const int quad_indices[] = {
@@ -15,7 +19,19 @@ static const int quad_indices[] = {
   1, 2, 3
 };
 
-unsigned int prepare_bg_rect() {
+void set_scale_factor(int width, int height, float *x, float *y) {
+  if (width > height) {
+    float ratio = (float)height / (float)width;
+    *x = ratio;
+    *y = 1.f;
+  } else {
+    float ratio = (float)width / (float)height;
+    *x = 1.f;
+    *y = ratio;
+  }
+}
+
+unsigned int prepare_bg(bool use_texture) {
   unsigned int vbo, vao, ebo;
   glGenVertexArrays(1, &vao);
   glGenBuffers(1, &vbo);
@@ -29,29 +45,55 @@ unsigned int prepare_bg_rect() {
   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);
+  glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void *)0);
+
+  if (use_texture) {
+    unsigned int texture;
+    int tex_width = 0, tex_height = 0;
+    unsigned char *tex_data = NULL;
+
+    glGenTextures(1, &texture);
+    glBindTexture(GL_TEXTURE_2D, texture);
+
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
+
+    tex_data = stbi_load("assets/sudoku-grid.png", &tex_width, &tex_height, NULL, 0);
+    if (tex_data) {
+      glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, tex_width, tex_height, 0, GL_RGB, GL_UNSIGNED_BYTE, tex_data);
+      glGenerateMipmap(GL_TEXTURE_2D);
+
+      stbi_image_free(tex_data);
+    } else {
+      printf("[ERROR] could not load texture image\n");
+    }
+
+    glEnableVertexAttribArray(1);
+    glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void *)(3 * sizeof(float)));
+  }
+
+  glBindVertexArray(0);
 
   return vao;
 }
 
-void draw_bg_rect(Shader shader, unsigned int vao, float* transform) {
-  use_shader(shader);
-
-  set_mat4(shader, "transform", transform);
-
-  glBindVertexArray(vao);
-  glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
-
-  // TODO: no idea why binding to default (0) breaks the grid shader
-  /* glBindVertexArray(0); */
-}
-
-void draw_bg_lines(Shader shader, float* transform, float resolution) {
+void draw_bg_grid_shader(Shader shader, int vao, float* transform, float resolution) {
   use_shader(shader);
 
   set_mat4(shader, "transform", transform);
   set_float(shader, "resolution", resolution);
 
-  glDrawArrays(GL_TRIANGLES, 0, 6);
+  glBindVertexArray(vao);
+  glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
+}
+
+void draw_bg_grid_texture(Shader shader, int vao, float* transform) {
+  use_shader(shader);
+  set_mat4(shader, "transform", transform);
+
+  glBindVertexArray(vao);
+  glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
 }