我正在开发一种软件,该软件可以将3D模型表面的工程数据可视化为彩色图。为此,我正在使用WebGL。目前,我能够在3D模型的表面上显示颜色。 但是现在我需要改善可视化效果,以在颜色之间进行尖锐过渡(在三角形表面上没有颜色插值)。 我不确定如何有效地做到这一点。
平滑轮廓图
清晰的轮廓图
答案 0 :(得分:0)
一种实现方法是将flat
interpolation modifier添加到您的color属性中,如this教程中所述。这样可以防止对颜色值进行插值,因此每个三角形只会以一种颜色(在三个顶点中的第一个顶点中指定)结束。
遗憾的是,我找不到关于它的webgl支持的任何信息,但您最好尝试一下它是否可以工作。
如果它不起作用或者您不希望看到单个三角形,也可以load the color data to a texture并获取片段着色器中每个像素的颜色。不过仍然会根据纹理大小进行一些插值(类似于放大后图像变得模糊)。
答案 1 :(得分:0)
不清楚您要做什么。您没有提供足够的信息来首先了解如何选择/计算颜色。
我只能猜出一些可能符合您描述的解决方案
采用后代技术的后期处理
您可以做一个简单的
gl_FragColor.rgb = floor(gl_FragColor.rgb * numLevels) / numLevels;
或者您可以在某些颜色空间中做到
// convert to HSV
vec3 hsv = rgb2hsv(gl_FragColor.rgb);
// quantize hue only
hsv.x = floor(hsv.x * numLevels) / numLevels;
// concert back to RGB
gl_FragColor.rgb = hsv2rgb(hsv);
或者您也可以在3D着色器中执行此操作,不必进行后期处理。
您可以找到rgb2hsv和hsv2rgb here,但是您当然可以使用其他颜色空间。
示例:
const gl = document.querySelector('canvas').getContext('webgl');
const m4 = twgl.m4;
const v3 = twgl.v3;
// used to generate colors
const ctx = document.createElement('canvas').getContext('2d');
ctx.canvas.width = 1;
ctx.canvas.height = 1;
const vs = `
attribute vec4 position;
attribute vec3 normal;
// note: there is no reason this has to come from an attrbute (per vertex)
// it could just as easily come from a texture used in the fragment shader
// for more resolution
attribute vec4 color;
uniform mat4 projection;
uniform mat4 modelView;
varying vec3 v_normal;
varying vec4 v_color;
void main () {
gl_Position = projection * modelView * position;
v_normal = mat3(modelView) * normal;
v_color = color;
}
`;
const fs = `
precision mediump float;
varying vec3 v_normal;
varying vec4 v_color;
uniform float numLevels;
uniform vec3 lightDirection;
vec3 rgb2hsv(vec3 c) {
vec4 K = vec4(0.0, -1.0 / 3.0, 2.0 / 3.0, -1.0);
vec4 p = mix(vec4(c.bg, K.wz), vec4(c.gb, K.xy), step(c.b, c.g));
vec4 q = mix(vec4(p.xyw, c.r), vec4(c.r, p.yzx), step(p.x, c.r));
float d = q.x - min(q.w, q.y);
float e = 1.0e-10;
return vec3(abs(q.z + (q.w - q.y) / (6.0 * d + e)), d / (q.x + e), q.x);
}
vec3 hsv2rgb(vec3 c) {
c = vec3(c.x, clamp(c.yz, 0.0, 1.0));
vec4 K = vec4(1.0, 2.0 / 3.0, 1.0 / 3.0, 3.0);
vec3 p = abs(fract(c.xxx + K.xyz) * 6.0 - K.www);
return c.z * mix(K.xxx, clamp(p - K.xxx, 0.0, 1.0), c.y);
}
void main() {
vec3 hsv = rgb2hsv(v_color.rgb);
hsv.x = floor(hsv.x * numLevels) / numLevels;
vec3 rgb = hsv2rgb(hsv);
// fake light
float light = dot(normalize(v_normal), lightDirection) * .5 + .5;
gl_FragColor = vec4(rgb * light, v_color.a);
// uncomment next line to see without hue quantization
// gl_FragColor = v_color;
}
`;
const programInfo = twgl.createProgramInfo(gl, [vs, fs]);
const radius = 5;
const thickness = 2;
const radialDivisions = 32;
const bodyDivisions = 12;
// creates positions, normals, etc...
const arrays = twgl.primitives.createTorusVertices(
radius, thickness, radialDivisions, bodyDivisions);
// add colors for each vertex
const numVerts = arrays.position.length / 3;
const colors = new Uint8Array(numVerts * 4);
for (let i = 0; i < numVerts; ++i) {
const pos = arrays.position.subarray(i * 3, i * 3 + 3);
const dist = v3.distance([3, 1, 3 + Math.sin(pos[0])], pos);
colors.set(hsla(clamp(dist / 10, 0, 1), 1, .5, 1), i * 4);
}
arrays.color = {
numComponents: 4,
data: colors,
};
// calls gl.createBuffer, gl.bindBuffer, gl.bufferData for each
// array in arrays
const bufferInfo = twgl.createBufferInfoFromArrays(gl, arrays);
twgl.resizeCanvasToDisplaySize(gl.canvas);
gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);
gl.enable(gl.DEPTH_TEST);
const aspect = gl.canvas.clientWidth / gl.canvas.clientHeight;
const halfHeight = 8;
const halfWidth = halfHeight * aspect;
const projection = m4.ortho(
-halfWidth, halfWidth,
-halfHeight, halfHeight,
-2, 2);
const modelView = m4.identity();
m4.rotateX(modelView, Math.PI * .5, modelView);
gl.useProgram(programInfo.program);
// calls gl.bindbuffer, gl.enableVertexAttribArray, gl.vertexAttribPointer
// for each attribute
twgl.setBuffersAndAttributes(gl, programInfo, bufferInfo);
// calls gl.activeTexture, gl.bindTexture, gl.uniformXXX
twgl.setUniforms(programInfo, {
projection,
modelView,
numLevels: 8,
lightDirection: v3.normalize([1, 2, 3]),
});
// calls gl.drawArrays or gl.drawElements
twgl.drawBufferInfo(gl, bufferInfo);
function hsla(h, s, l, a) {
ctx.fillStyle = `hsla(${h * 360 | 0},${s * 100 | 0}%,${l * 100 | 0}%,${a})`;
ctx.fillRect(0, 0, 1, 1);
return ctx.getImageData(0, 0, 1, 1).data;
}
function clamp(v, min, max) {
return Math.min(max, Math.max(min, v));
}
body { margin: 0; }
canvas { width: 100vw; height: 100vh; display: block; }
<script src="https://twgljs.org/dist/4.x/twgl-full.min.js"></script>
<canvas></canvas>
在1个通道中渲染,使用查找表
在这种情况下,您将使用N种颜色制作Nx1纹理。然后在着色器中,您只需计算一个灰度等级(目前尚不清楚如何着色),然后使用它来从纹理中查找颜色
uniform sampler2D lookupTable; // Nx1 texture set to nearest filtering
float gray = whateverYourDoingNow();
vec4 color = texture2D(lookupTable, vec2((gray, 0.5);
// apply lighting to color
...
示例:
const gl = document.querySelector('canvas').getContext('webgl');
const m4 = twgl.m4;
const v3 = twgl.v3;
const vs = `
attribute vec4 position;
attribute vec3 normal;
// note: there is no reason this has to come from an attrbute (per vertex)
// it could just as easily come from a texture used in the fragment shader
// for more resolution
attribute float hotness; // the data value 0 to 1
uniform mat4 projection;
uniform mat4 modelView;
varying vec3 v_normal;
varying float v_hotness;
void main () {
gl_Position = projection * modelView * position;
v_normal = mat3(modelView) * normal;
v_hotness = hotness;
}
`;
const fs = `
precision mediump float;
varying vec3 v_normal;
varying float v_hotness;
uniform float numColors;
uniform sampler2D lookupTable;
uniform vec3 lightDirection;
void main() {
vec4 color = texture2D(lookupTable, vec2(v_hotness, 0.5));
// fake light
float light = dot(normalize(v_normal), lightDirection) * .5 + .5;
gl_FragColor = vec4(color.rgb * light, color.a);
}
`;
const programInfo = twgl.createProgramInfo(gl, [vs, fs]);
const radius = 5;
const thickness = 2;
const radialDivisions = 32;
const bodyDivisions = 12;
// creates positions, normals, etc...
const arrays = twgl.primitives.createTorusVertices(
radius, thickness, radialDivisions, bodyDivisions);
// add a hotness value, 0 <-> 1, for each vertex
const numVerts = arrays.position.length / 3;
const hotness = [];
for (let i = 0; i < numVerts; ++i) {
const pos = arrays.position.subarray(i * 3, i * 3 + 3);
const dist = v3.distance([3, 1, 3 + Math.sin(pos[0])], pos);
hotness[i] = clamp(dist / 10, 0, 1);
}
arrays.hotness = {
numComponents: 1,
data: hotness,
};
// calls gl.createBuffer, gl.bindBuffer, gl.bufferData for each
// array in arrays
const bufferInfo = twgl.createBufferInfoFromArrays(gl, arrays);
const colors = [
255, 0, 0, 255, // red
255, 150, 30, 255, // orange
255, 255, 0, 255, // yellow
0, 210, 0, 255, // green
0, 255, 255, 255, // cyan
0, 0, 255, 255, // blue
160, 30, 255, 255, // purple
255, 0, 255, 255, // magenta
];
// calls gl.createTexture, gl.texImage2D, gl.texParameteri
const lookupTableTexture = twgl.createTexture(gl, {
src: colors,
width: colors.length / 4,
wrap: gl.CLAMP_TO_EDGE,
minMag: gl.NEAREST, // comment this line out to see non hard edges
});
twgl.resizeCanvasToDisplaySize(gl.canvas);
gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);
gl.enable(gl.DEPTH_TEST);
const aspect = gl.canvas.clientWidth / gl.canvas.clientHeight;
const halfHeight = 8;
const halfWidth = halfHeight * aspect;
const projection = m4.ortho(
-halfWidth, halfWidth,
-halfHeight, halfHeight,
-2, 2);
const modelView = m4.identity();
m4.rotateX(modelView, Math.PI * .5, modelView);
gl.useProgram(programInfo.program);
// calls gl.bindbuffer, gl.enableVertexAttribArray, gl.vertexAttribPointer
// for each attribute
twgl.setBuffersAndAttributes(gl, programInfo, bufferInfo);
// calls gl.activeTexture, gl.bindTexture, gl.uniformXXX
twgl.setUniforms(programInfo, {
projection,
modelView,
lookupTable: lookupTableTexture,
lightDirection: v3.normalize([1, 2, 3]),
});
// calls gl.drawArrays or gl.drawElements
twgl.drawBufferInfo(gl, bufferInfo);
function clamp(v, min, max) {
return Math.min(max, Math.max(min, v));
}
body { margin: 0; }
canvas { width: 100vw; height: 100vh; display: block; }
<script src="https://twgljs.org/dist/4.x/twgl-full.min.js"></script>
<canvas></canvas>