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

shaders/board_f.glsl

@@ -1,6 +1,10 @@
 #version 330 core
 out vec4 FragColor;
 
+in vec2 texCoords;
+
+uniform sampler2D aTexture;
+
 void main() {
-  FragColor = vec4(240.f/255.f, 235.f/255.f, 227.f/255.f, 1.0);
+  FragColor = texture(aTexture, texCoords);
 }

shaders/board_v.glsl

@@ -1,8 +1,11 @@
 #version 330 core
 layout (location = 0) in vec3 aPos;
+layout (location = 1) in vec2 aTexCoords;
+out vec2 texCoords;
 
 uniform mat4 transform;
 
 void main() {
   gl_Position = transform * vec4(aPos, 1.0f);
+  texCoords = aTexCoords;
 }

shaders/grid_f.glsl

@@ -15,12 +15,14 @@ void main()
 
     // Calculate the UV coordinates of the current fragment
     vec2 uv = (gl_FragCoord * transform).xy / vec2(resolution, resolution); // Adjust the resolution as needed
+    float scale_x = transform[0][0];
+    float scale_y = transform[1][1];
 
     // Calculate the coordinates of the current fragment in the [-1, 1] range
-    float fragCoordX = (uv.x - 0.5) * (2.0 / transform[0][0]) - 1.0;
-    float fragCoordY = (uv.y - 0.5) * (2.0 / transform[1][1]) - 1.0;
+    float fragCoordX = (uv.x - 0.5) * (2.0 / scale_x) - 1.0;
+    float fragCoordY = (uv.y - 0.5) * (2.0 / scale_y) - 1.0;
     
-    // Initialize colors for grid lines and background
+    // Colors for grid lines
     vec3 gridColor = vec3(0.4, 0.4, 0.4);
     vec3 gridColorThick = vec3(0.2, 0.2, 0.2);
 
@@ -42,6 +44,6 @@ void main()
     } else if (isGridX || isGridY) {
         FragColor = vec4(gridColor, 1.0);
     } else {
-        discard;
+        FragColor = vec4(240.f/255.f, 235.f/255.f, 227.f/255.f, 1.0);
     }
 }

shaders/grid_v.glsl

@@ -1,12 +0,0 @@
-#version 330 core
-uniform mat4 transform;
-
-vec3 gridPlane[6] = vec3[](
-    vec3(1, 1, 0), vec3(-1, -1, 0), vec3(-1, 1, 0),
-    vec3(-1, -1, 0), vec3(1, 1, 0), vec3(1, -1, 0)
-);
-
-void main() {
-  vec3 p = gridPlane[gl_VertexID].xyz;
-  gl_Position = vec4(p, 1.0f);
-}