What This Calculation Does:
1. The Problem:
When a ray hits a wall, we need to know where exactly along that wall face the hit occurred. This determines which part of the texture to display.
2. World Coordinates vs Block-Relative Coordinates:
- World coordinate: Absolute position in the game world (e.g., x = 192)
- Block-relative coordinate: Position within the current block (0.0 to 1.0)
3. The fmod() Function:
fmod(ray_x, BLOCK) gives the remainder when dividing ray_x by BLOCK:
- If ray_x = 192 and BLOCK = 64: fmod(192, 64) = 0 (192 = 3×64 + 0)
- If ray_x = 200 and BLOCK = 64: fmod(200, 64) = 8 (200 = 3×64 + 8)
- If ray_x = 127 and BLOCK = 64: fmod(127, 64) = 63 (127 = 1×64 + 63)
4. Normalizing to 0.0-1.0:
Dividing by BLOCK converts the remainder to a fraction:
- 0.0 = Left edge of the block
- 0.5 = Middle of the block
- 1.0 = Right edge of the block
5. Why This Matters for Textures:
- Texture mapping: The 0.0-1.0 value directly maps to texture coordinates
- Seamless walls: Adjacent blocks align perfectly
- Consistent scaling: Works regardless of BLOCK size
- Easy calculation: Simple modulo operation
6. Example Usage:
If texture is 64 pixels wide and wall_hit = 0.75:
texture_x = (int)(0.75 * 64) = 48
So we'd use column 48 of the texture for this wall strip.