标记为 OpenGL,因为问题应该与 OpenGL/WebGL 无关
我正在尝试实现基于着色器的纹理过滤。我有 之前的问题 和一个答案,帮助我修复了选择 mip 级别时的错误。实际上,该示例在 mip 级别之间执行“最近”操作。
现在我想在级别之间进行双线性过滤(NEAREST_MIPMAP_LINEAR)。
以前面的示例为例,它计算一个
mipLevel
然后就这样了
outColor = colors[int(mipLevel)]
其中
colors
是 8 种 vec4 颜色的数组,与相应纹理的 mip 级别的颜色相匹配。该示例在左侧使用纹理绘制,在右侧使用此颜色表并调整纹理坐标以强制选择 mip 级别。
根据规范第 3.8.10.4 节,在 mip 级别之间插值的公式为
τ = [1 − frac(λ)]τ1 + frac(λ)τ2.
其中 λ 是上面的
mipLevel
,τ1
和 τ2
是来自 mip 级别的颜色。好像只能翻译成这个
t1 = colors[int(mipLevel)];
t2 = colors[int(mipLevel)];
outColor = mix(t1, t2, fract(mipLevel));
但是当我尝试时,输出与硬件的实际过滤不匹配。下面,如果它正常工作,两侧应该同步改变颜色。
我错过了什么?
html, body {
margin: 0;
font-family: monospace;
height: 100%;
}
canvas {
display: block;
width: 100%;
height: 100%;
}
<canvas id="c"></canvas>
<script type="module">
import * as twgl from 'https://twgljs.org/dist/5.x/twgl-full.module.js';
const vs = `#version 300 es
uniform mat4 u_worldViewProjection;
uniform mat3 u_texMat;
out vec2 v_texCoord;
const vec2 position[6] = vec2[6](
vec2(0, 0),
vec2(1, 0),
vec2(0, 1),
vec2(0, 1),
vec2(1, 0),
vec2(1, 1));
void main() {
vec2 p = position[gl_VertexID];
v_texCoord = (u_texMat * vec3(p, 1)).xy;
gl_Position = u_worldViewProjection * vec4(p, 0, 1);
}
`;
const fsTex = `#version 300 es
precision highp float;
in vec2 v_texCoord;
uniform sampler2D u_tex;
out vec4 outColor;
void main() {
outColor = texture(u_tex, v_texCoord);
}
`;
const fsMipLevel = `#version 300 es
precision highp float;
in vec2 v_texCoord;
out vec4 outColor;
const vec4 colors[8] = vec4[8](
vec4( 1, 0, 0, 1), // 0: red
vec4( 1, 1, 0, 1), // 1: yellow
vec4( 0, 1, 0, 1), // 2: green
vec4( 0, 1, 1, 1), // 3: cyan
vec4( 0, 0, 1, 1), // 4: blue
vec4( 1, 0, 1, 1), // 5: magenta
vec4(0.5, 0.5, 0.5, 1), // 6: gray
vec4( 1, 1, 1, 1));// 7: white
void main() {
vec2 size = vec2(128.0, 128.0); // size of the texture in your example
vec2 dx = dFdx(v_texCoord * size);
vec2 dy = dFdy(v_texCoord * size);
float deltaMaxSq = max(dot(dx, dx), dot(dy, dy));
float mipLevel = 0.5 * log2(deltaMaxSq) + 0.5;
vec4 t1 = colors[int(mipLevel)];
vec4 t2 = colors[int(mipLevel + 1.0)];
outColor = mix(t1, t2, fract(mipLevel));
}
`;
const colors = [
'#F00',
'#FF0',
'#0F0',
'#0FF',
'#00F',
'#F0F',
'#888',
'#FFF',
];
function createMips(colors) {
const ctx = document.createElement('canvas').getContext('2d');
const numMips = colors.length;
return colors.map((color, i) => {
const size = 2 ** (numMips - i - 1);
ctx.canvas.width = size;
ctx.canvas.height = size;
ctx.fillStyle = color;
ctx.fillRect(0, 0, size, size);
return ctx.getImageData(0, 0, size, size);
});
}
function main() {
const m4 = twgl.m4;
const gl = document.getElementById("c").getContext("webgl2");
if (!gl) {
alert("Sorry, this example requires WebGL 2.0"); // eslint-disable-line
return;
}
const texProgramInfo = twgl.createProgramInfo(gl, [vs, fsTex]);
const mipProgramInfo = twgl.createProgramInfo(gl, [vs, fsMipLevel]);
const texImage = gl.createTexture();
gl.bindTexture(gl.TEXTURE_2D, texImage);
const data = createMips(colors);
data.forEach(({width, height, data}, level) => {
gl.texImage2D(gl.TEXTURE_2D, level, gl.RGBA8, width, height, 0, gl.RGBA, gl.UNSIGNED_BYTE, data);
});
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST_MIPMAP_LINEAR);
const lerp = (a, b, t) => a + (b - a) * t;
function render(time) {
time *= 0.001;
twgl.resizeCanvasToDisplaySize(gl.canvas);
gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);
gl.clearColor(0.3, 0.3, 0.3, 1);
gl.clear(gl.COLOR_BUFFER_BIT);
const uniforms = {};
const s = lerp(1, 128, Math.sin(time) * 0.5 + 0.5);
uniforms.u_texMat = [
s, 0, 0,
0, s, 0,
0, 0, 1,
];
uniforms.u_worldViewProjection = m4.translation([-1.01, -0.5, 0]);
gl.useProgram(texProgramInfo.program);
twgl.setUniforms(texProgramInfo, uniforms);
gl.drawArrays(gl.TRIANGLES, 0, 6);
uniforms.u_worldViewProjection = m4.translation([0.01, -0.5, 0]);
gl.useProgram(mipProgramInfo.program);
twgl.setUniforms(mipProgramInfo, uniforms);
gl.drawArrays(gl.TRIANGLES, 0, 6);
requestAnimationFrame(render);
}
requestAnimationFrame(render);
}
main();
</script>
对于“NEAREST”过滤,您必须对索引进行舍入(如名称“NEAREST”所示):
c[round(l)]
但是,使用“线性”过滤,您必须在下一个较小索引和下一个较大索引的颜色之间进行插值:
mix(c[int(l)], c[int(l)+1], fract(l))
所以你必须删除
+ 0.5
:
float mipLevel = 0.5 * log2(deltaMaxSq) + 0.5;
float mipLevel = 0.5 * log2(deltaMaxSq);