Masking OpenGL texture by a pattern
- by user1304844
Tiled terrain. User wants to build a structure. He presses build and for each tile there is an "allow" or "disallow" tile sprite added to the scene. FPS drops right away, since there are 600+ tiles added to the screen. Since map equals screen, there is no scrolling. I came to an idea to make an allow grid covering the whole map and mask the disallow fields.
Approach 1:
Create allow and disallow grid textures.
Draw a polygon on screen.
Pass both textures to the fragment shader.
Determine the position inside the polygon and use color from allowTexture if the fragment belongs to the allow field, disallow otherwise
Problem: How do I know if I'm on the field that isn't allowed if I cannot pass the matrix representing the map (enum FieldStatus[][] (Allow / Disallow)) to the shader? Therefore, inside the shader I don't know which fragments should be masked.
Approach 2:
Create allow texture.
Create an empty texture buffer same size as the allow texture
Memset the pixels of the empty texture to desired color for each pixel that doesn't allow building.
Draw a polygon on screen.
Pass both textures to the fragment shader.
Use texture2 color if alpha 0, texture1 color otherwise.
Problem: I'm not sure what is the right way to manipulate pixels on a texture. Do I just make a buffer with width*height*4 size and memcpy the color[] to desired coordinates or is there anything else to it? Would I have to call glTexImage2D after every change to the texture?
Another problem with this approach is that it takes a lot more work to get a prettier effect since I'm manipulating the color pixels instead of just masking two textures.
varying vec2 TexCoordOut;
uniform sampler2D Texture1;
uniform sampler2D Texture2;
void main(void){
vec4 allowColor = texture2D(Texture1, TexCoordOut);
vec4 disallowColor = texture2D(Texture2, TexCoordOut);
if(disallowColor.a > 0){
gl_FragColor= disallowColor;
}else{
gl_FragColor= allowColor;
}}
I'm working with OpenGL on Windows. Any other suggestion is welcome.
