Unity TileMap Shader瓦片接缝灰线问题求助

Hey there! Let's tackle those annoying tile seam lines you're dealing with. You’re absolutely right to suspect floating-point precision issues—this is a super common gotcha with tile mapping shaders, especially when sampling from a spritesheet and doing UV calculations that can drift slightly due to floating-point errors. Let’s break down the fixes step by step:

1. Fix UV & Tile Index Precision #

Your current index calculation and UV mod operations are prone to tiny precision errors that can push sampling just over a tile boundary. Here’s how to tighten that up:

• Replace the % operator with frac() for more reliable fractional UV extraction—frac() is designed exactly for getting the decimal part of a float, which avoids edge-case errors with mod.
• Add a tiny offset when converting UV to integer tile coordinates to prevent floor() from rounding down incorrectly due to precision drift.
• Clamp your tile coordinates to avoid index out-of-bounds issues (which can cause random wrong tiles/seams).

2. Add Texture Padding (The Most Reliable Fix) #

Most tile seam gray lines come from texture filtering (like linear filtering) sampling pixels from adjacent tiles in your spritesheet. To fix this, add 1-pixel padding around each tile in your _DiffuseTex spritesheet, matching the edge color of the tile. Then adjust your shader to sample only the inner tile area, skipping the padding.

Modified Shader Fragment Code #

Here’s the updated frag function incorporating these fixes:

fixed4 frag (v2f i) : SV_Target {
    float mapSizeModif = 1.0f / _MapWidth;
    float worldSizeModif = 1.0f / _WorldWidth;
    float maskMapSizeModif = 1.0f / _MaskMapWidth;

    float lightness = 1.0f;

    // Fix tile index precision with offset + clamping
    float2 worldUV = i.uv * _WorldWidth;
    uint x = (uint)clamp(floor(worldUV.x + 0.0001f), 0, _WorldWidth - 1);
    uint y = (uint)clamp(floor(worldUV.y + 0.0001f), 0, _WorldWidth - 1);
    uint index = x + y * _WorldWidth;

    // Use frac() for clean local tile UV instead of mod
    float2 tileLocalUV = frac(worldUV) * worldSizeModif;

    uint id = (uint)_allIDs[index];

    // Base UV position for the tile in the spritesheet
    float2 tileBaseUV = float2(
        mapSizeModif * (id % _MapWidth),
        mapSizeModif * floor(((float)id)/_MapWidth)
    );

    // Adjust for texture padding (tweak values to match your spritesheet)
    // Example: 1px padding on a 256x256 spritesheet = 1/256 = 0.00390625
    float tilePadding = 0.00390625; 
    float tileScale = (mapSizeModif - 2 * tilePadding) / mapSizeModif;
    tileLocalUV = tileLocalUV * tileScale + tilePadding;

    // Combine base and local UVs for final sampling
    float2 finalUV = tileBaseUV + tileLocalUV;

    fixed4 col = tex2D(_DiffuseTex, finalUV);
    col *= _GlobalLumosity;
    col *= _GlobalHue;
    col.a = lightness;

    return col;
}

Extra Quick Checks #

• Set your _DiffuseTex wrap mode to Clamp in the Unity inspector—this prevents accidental sampling of distant tiles if UVs drift slightly.
• If you can’t add padding right away, switch the texture’s filter mode to Point (no filter)—this eliminates filtering-induced seams but makes tiles look pixelated (use this as a temporary test to confirm the issue is filtering-related).

Key Notes #

• The tilePadding value depends on your spritesheet size: for a 512x512 sheet, 1px padding is 1/512 = 0.001953125. Make this a Shader property if you want to adjust it without re-compiling.
• The precision fixes alone might reduce seams, but combining them with texture padding will fully resolve the issue in most cases.

内容的提问来源于stack exchange，提问作者Polymer