javascript - 尽管禁用 mipmap 和半像素校正，纹理仍然出血

Question

我已经应用了此答案 https://gamedev.stackexchange.com/questions/46963/how-to-avoid-texture-bleeding-in-a-texture-atlas 中给出的两个必要步骤，但我仍然会出现纹理渗色。

我有一个在边界处填充了纯色的图集:x y w h: 0 0 32 32, 0 32 32 32, 0 64 32 32, 0 32 * 3 32 32

我想使用 webgl 显示每个帧，而无需纹理渗色，仅按原样显示纯色。

我已禁用 mipmaping:

gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.REPEAT);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.REPEAT);

//gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR_MIPMAP_LINEAR);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);

我应用了半像素校正:

  const uvs = (src, frame) => {
    const tw = src.width,
          th = src.height;

    const getTexelCoords = (x, y) => {
      return [(x + 0.5) / tw, (y + 0.5) / th];
    };

    let frameLeft = frame[0],
        frameRight = frame[0] + frame[2],
        frameTop = frame[1],
        frameBottom = frame[1] + frame[3];

    let p0 = getTexelCoords(frameLeft, frameTop),
        p1 = getTexelCoords(frameRight, frameTop),
        p2 = getTexelCoords(frameRight, frameBottom),
        p3 = getTexelCoords(frameLeft, frameBottom);

    return [
      p0[0], p0[1],
      p1[0], p1[1],
      p3[0], p3[1],
      p2[0], p2[1]
    ];
  };

但我仍然会出现纹理渗色。起初我尝试使用 pixi.js，也遇到了纹理渗色，然后我尝试使用 vanilla js。

我已经通过更改这些行解决了这个问题:

    let frameLeft = frame[0],
        frameRight = frame[0] + frame[2] - 1,
        frameTop = frame[1],
        frameBottom = frame[1] + frame[3] - 1;

如您所见，我从右边缘和下边缘减去 1。以前这些索引是 32，这意味着另一帧的开始，现在必须改为 31。我不知道这是否是正确的解决方案。

Answer 1

您的解决方案是正确的。

假设我们有一个 4x2 纹理和两个 2x2 像素 Sprite

+-------+-------+-------+-------+
|       |       |       |       |
|   E   |   F   |   G   |   H   |
|       |       |       |       |
+-------+-------+-------+-------+
|       |       |       |       |
|   A   |   B   |   C   |   D   |
|       |       |       |       |
+-------+-------+-------+-------+

字母代表纹理中像素的中心。

(pixelCoord + 0.5) / textureDimensions

在 A、B、E、F 处选取 2x2 Sprite 。如果您的纹理坐标位于 B 和 C 之间的任何位置，那么如果您启用了纹理过滤，您就会得到一些 C 的混合。

最初，您计算的是坐标 A，A + 宽度，其中宽度 = 2。这会引导您从 A 一直到 C。通过添加 -1，您将得到 A 到 B。

不幸的是，您遇到了一个新问题，即您只显示了 A 和 B 的一半。您可以通过填充 Sprite 来解决这个问题。例如，将其设置为 6x2，其中像素是重复的 Sprite 的边缘

+-------+-------+-------+-------+-------+-------+
|       |       |       |       |       |       |
|   E   |   F   |   Fr  |   Gr  |   G   |   H   |
|       |       |       |       |       |       |
+-------+-------+-------+-------+-------+-------+
|       |       |       |       |       |       |
|   A   |   B   |   Br  |   Cr  |   C   |   D   |
|       |       |       |       |       |       |
+-------+-------+-------+-------+-------+-------+

上面的 Br 是 B 重复，Cr 是 C 重复。将重复设置为 gl.CLAMP_TO_EDGE 将为您重复 A 和 D。现在您可以使用边缘了。

Sprite CDGH 的坐标为

p0 = 4 / texWidth
p1 = 0 / texHeigth
p2 = (4 + spriteWidth) / texWidth
p3 = (0 + spriteHeigth) / texHeight

查看差异的最佳方法是使用未填充和填充两种技术绘制 2 个大 Sprite 。

const numSprites = 3;
const spriteSize = 16;
const m4 = twgl.m4;
const gl = document.querySelector('canvas').getContext('webgl');

const spriteElem = makeSprites();
log('sprites');
document.body.appendChild(spriteElem);
const paddedSpriteElem = padSprites(spriteElem);
log('padded sprites');
document.body.appendChild(paddedSpriteElem);

const unpaddedTex = twgl.createTexture(gl, {src: spriteElem, wrap: gl.CLAMP_TO_EDGE, minMax: gl.LINEAR});
const paddedTex = twgl.createTexture(gl, {src: paddedSpriteElem, wrap: gl.CLAMP_TO_EDGE, minMax: gl.LINEAR});

const vs = `
attribute vec4 position;
attribute vec2 texcoord;
varying vec2 v_texcoord;
uniform mat4 matrix;
void main() {
  gl_Position = matrix * position;
  v_texcoord = texcoord;
}
`;

const fs = `
precision highp float;
varying vec2 v_texcoord;
uniform sampler2D tex;
void main() {
  gl_FragColor = texture2D(tex, v_texcoord);
}
`;

const program = twgl.createProgram(gl, [vs, fs]);
gl.useProgram(program);

const ploc = gl.getAttribLocation(program, 'position');
const tloc = gl.getAttribLocation(program, 'texcoord');
const mloc = gl.getUniformLocation(program, 'matrix');
// no need to look up 'tex' as we're only using 1 texture and uniforms default
// to 0 so it will use texture unit 0, the default

const pbuf = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, pbuf);
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([0, 1, 1, 1, 0, 0, 1, 0]), gl.STATIC_DRAW);
gl.enableVertexAttribArray(ploc);
gl.vertexAttribPointer(ploc, 2, gl.FLOAT, false, 0, 0);

const tbuf = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, tbuf);
gl.enableVertexAttribArray(tloc);
gl.vertexAttribPointer(tloc, 2, gl.FLOAT, false, 0, 0);

const ibuf = gl.createBuffer();
gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, ibuf);
gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint8Array([0, 1, 2, 2, 1, 3]), gl.STATIC_DRAW);

gl.clearColor(0, 0, 0, 1);
gl.clear(gl.COLOR_BUFFER_BIT);

// un paddded using rect from centers
{
   const spriteId = 1;
   const texWidth = spriteElem.width;
   const texHeight = spriteElem.height;
   const x = spriteId * spriteSize;
   const y = 0;
   const p0x = (x + 0.5) / texWidth;
   const p0y = (y + 0.5) / texHeight;
   const p1x = (x + spriteSize - 1 + 0.5) / texWidth;
   const p1y = (y + spriteSize - 1 + 0.5) / texHeight;
   gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([
     p0x, p0y,
     p1x, p0y,
     p0x, p1y,
     p1x, p1y,
   ]), gl.STATIC_DRAW);
   gl.bindTexture(gl.TEXTURE_2D, unpaddedTex);
   
   let m = m4.ortho(0, gl.canvas.width, 0, gl.canvas.height, -1, 1);
   m = m4.translate(m, [2, 5, 0]);
   m = m4.scale(m, [96, 96, 1]);
   gl.uniformMatrix4fv(mloc, false, m);
   gl.drawElements(gl.TRIANGLES, 6, gl.UNSIGNED_BYTE, 0);
}

// paddded using rect from edges
{
   const spriteId = 1;
   const texWidth = paddedSpriteElem.width;
   const texHeight = paddedSpriteElem.height;
   const x = spriteId * (spriteSize + 2);
   const y = 0;
   const p0x = (x) / texWidth;
   const p0y = (y) / texHeight;
   const p1x = (x + spriteSize) / texWidth;
   const p1y = (y + spriteSize) / texHeight;
   gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([
     p0x, p0y,
     p1x, p0y,
     p0x, p1y,
     p1x, p1y,
   ]), gl.STATIC_DRAW);
   gl.bindTexture(gl.TEXTURE_2D, paddedTex);
   
   let m = m4.ortho(0, gl.canvas.width, 0, gl.canvas.height, -1, 1);
   m = m4.translate(m, [102, 5, 0]);
   m = m4.scale(m, [96, 96, 1]);
   gl.uniformMatrix4fv(mloc, false, m);
   gl.drawElements(gl.TRIANGLES, 6, gl.UNSIGNED_BYTE, 0);
}

// unpaddded using rect from edges (bleeding)
{
   const spriteId = 1;
   const texWidth = spriteElem.width;
   const texHeight = spriteElem.height;
   const x = spriteId * spriteSize;
   const y = 0;
   const p0x = (x) / texWidth;
   const p0y = (y) / texHeight;
   const p1x = (x + spriteSize) / texWidth;
   const p1y = (y + spriteSize) / texHeight;
   gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([
     p0x, p0y,
     p1x, p0y,
     p0x, p1y,
     p1x, p1y,
   ]), gl.STATIC_DRAW);
   gl.bindTexture(gl.TEXTURE_2D, unpaddedTex);
   
   let m = m4.ortho(0, gl.canvas.width, 0, gl.canvas.height, -1, 1);
   m = m4.translate(m, [202, 5, 0]);
   m = m4.scale(m, [96, 96, 1]);
   gl.uniformMatrix4fv(mloc, false, m);
   gl.drawElements(gl.TRIANGLES, 6, gl.UNSIGNED_BYTE, 0);
}

function padSprites(elem) {
  const canvas = document.createElement('canvas');
  canvas.className = 'zoom';
  canvas.width = numSprites * spriteSize + (2 * numSprites - 1);
  canvas.height = spriteSize;
  const ctx = canvas.getContext('2d');
  let dstX = 0;
  const offsets = [
    // corners
    [-1, -1],
    [ 1, -1],
    [-1,  1],
    [ 1,  1],
    // edges
    [-1,  0],
    [ 1,  0],
    [ 0, -1],
    [ 0,  1],
    // middle
    [ 0,  0],
  ];
  for (let i = 0; i < numSprites; ++i) {
    const srcX = i * spriteSize;
    for (const offset of offsets) {
      ctx.drawImage(
        elem,
        srcX, 0, spriteSize, spriteSize,
        dstX + offset[0], offset[1], spriteSize, spriteSize,
      );    
    }
    dstX += spriteSize + 2;
  }
  return canvas;
}

function makeSprites() {
  const canvas = document.createElement('canvas');
  canvas.width = numSprites * spriteSize;
  canvas.height = spriteSize;
  canvas.className = 'zoom';
  const ctx = canvas.getContext('2d');
  ctx.font = '12px sans-serif';
  ctx.textAlign = 'center';
  ctx.textBaseline = 'middle';
  for (let i = 0; i < numSprites; ++i) {
    const x = spriteSize * i;
    const h = i / numSprites;
    ctx.fillStyle = hsl(h, 1, 0.4);
    ctx.fillRect(x, 0, spriteSize, spriteSize);
    ctx.fillStyle = hsl(h, 1, 0.85);
    for (let j = 0; j < spriteSize; j += 4) {
      ctx.fillRect(x + j, 0, 2, 2);
      ctx.fillRect(x, j, 2, 2);
      ctx.fillRect(x + j, spriteSize - 2, 2, 2);
      ctx.fillRect(x + spriteSize - 2, j, 2, 2);
    }
    ctx.fillStyle = hsl(h + 0.5, 1, 0.5);
    ctx.fillRect(x + 1, 1, spriteSize - 2, spriteSize - 2);
    ctx.fillStyle = hsl(h, 1, 0.5);
    ctx.fillText(String.fromCharCode(65 + i), x + spriteSize / 2, spriteSize / 2);
  }
  return canvas;
}

function hsl(h, s, l) {
  return `hsl(${h * 360},${s * 100}%,${l * 100}%)`;
}

function log(...args) {
  const elem = document.createElement('pre');
  elem.textContent = [...args].join(' ');
  document.body.appendChild(elem);
}

canvas {
  display: block;
  image-rendering: pixelated;
  padding: 5px;
}
.zoom {
  zoom: 4;
}

<script src="https://twgljs.org/dist/4.x/twgl-full.min.js"></script>
<pre>left  : rect from centers using unpadded texture
middle: rect from edges using padded texture
right : rect from edges using unpadded texture (bleeding)
 (note the red at the bottom left edge)</pre>
<canvas></canvas>