How do I determine if a tile is a slope based on the tile image?

Question

In my game, every tile is a 32x32 texture. All the slopes are a 0 - 45 degree angle. I would like to determine, at the time I load the tile, if the is sloped by examining its texture/bitmap data. How can I do this?

Answer 1

Every tile is a 32x32 texture. All the slopes are a 0 - 45 degree angle. And yes I'm determining the slope at load time only.

Under this assumption, and that other non-slope tiles won't have strange variations, the simplest solution I can think of is the following.

• If blue pixel is empty and purple pixel is filled, the tile is a right slope.
• If green pixel is filled and yellow pixel is empty, the tile is a left slope.

If you're using alpha transparency on your tiles, you can check if a pixel is empty by seeing if its alpha value is 0.

In pseudocode:

s = image size
if(image[0,s-2].alpha == 0 && image[s-1,0].alpha != 0)
{
    // Right Slope
}
else if(image[0,0].alpha != 0 && image[s-1,s-2].alpha == 0)
{
    // Left Slope
}

As for getting the color at specific pixel on a texture, check the OpenGL API.