是否可以像纹理一样对默认颜色缓冲区进行采样？
我想做这样的事情：
我不想渲染到帧缓冲区的原因是，WebGL在使用默认颜色缓冲区时具有多重采样，但对于帧缓冲区却没有。一个好的解决方案是渲染到默认缓冲区，然后将其复制到帧缓冲区或纹理，但是我不确定是否可行。
答案 0 :(得分：1)
您无法直接从默认颜色缓冲区中采样，但是它附带的默认 framebuffer 恰好是 framebuffer ，您可以调用{{1} }，然后将内容复制到当前绑定的活动纹理。
copyTexImage2D
// initializing the texture
const targetTexture = gl.createTexture();
gl.bindTexture(gl.TEXTURE_2D, targetTexture);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
// in your render loop
gl.bindFramebuffer(gl.FRAMEBUFFER, null);
gl.bindTexture(gl.TEXTURE_2D, targetTexture);
gl.copyTexImage2D(
gl.TEXTURE_2D, //target
0, // mip level, has to be zero for default framebuffer
gl.RGBA, // pixel format, default framebuffer is RGBA if the context was created with alpha false you need to use RGB
0, 0, // x,y
gl.drawingBufferWidth, // width
gl.drawingBufferHeight, // height
0 // border, always 0
);
// WebGL - Copy Default Framebuffer
// from https://stackoverflow.com/questions/55228453/sample-default-webgl-color-buffer/
// based on https://webglfundamentals.org/webgl/webgl-render-to-texture.html
"use strict";
function main() {
// Get A WebGL context
/** @type {HTMLCanvasElement} */
var canvas = document.getElementById("canvas");
var gl = canvas.getContext("webgl");
if (!gl) {
return;
}
// setup GLSL program
var program = webglUtils.createProgramFromScripts(gl, ["3d-vertex-shader", "3d-fragment-shader"]);
// look up where the vertex data needs to go.
var positionLocation = gl.getAttribLocation(program, "a_position");
var texcoordLocation = gl.getAttribLocation(program, "a_texcoord");
// lookup uniforms
var matrixLocation = gl.getUniformLocation(program, "u_matrix");
var textureLocation = gl.getUniformLocation(program, "u_texture");
// Create a buffer for positions
var positionBuffer = gl.createBuffer();
// Bind it to ARRAY_BUFFER (think of it as ARRAY_BUFFER = positionBuffer)
gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
// Put the positions in the buffer
setGeometry(gl);
// provide texture coordinates for the rectangle.
var texcoordBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, texcoordBuffer);
// Set Texcoords.
setTexcoords(gl);
// Create a texture.
var texture = gl.createTexture();
gl.bindTexture(gl.TEXTURE_2D, texture);
{
// fill texture with 3x2 pixels
const level = 0;
const internalFormat = gl.LUMINANCE;
const width = 3;
const height = 2;
const border = 0;
const format = gl.LUMINANCE;
const type = gl.UNSIGNED_BYTE;
const data = new Uint8Array([
128, 64, 128,
0, 192, 0,
]);
const alignment = 1;
gl.pixelStorei(gl.UNPACK_ALIGNMENT, alignment);
gl.texImage2D(gl.TEXTURE_2D, level, internalFormat, width, height, border,
format, type, data);
// set the filtering so we don't need mips and it's not filtered
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
}
// Create a texture to render to
const targetTextureWidth = gl.drawingBufferWidth;
const targetTextureHeight = gl.drawingBufferHeight;
const targetTexture = gl.createTexture();
gl.bindTexture(gl.TEXTURE_2D, targetTexture);
{
// define size and format of level 0
const level = 0;
const internalFormat = gl.RGBA;
const border = 0;
const format = gl.RGBA;
const type = gl.UNSIGNED_BYTE;
const data = null;
gl.texImage2D(gl.TEXTURE_2D, level, internalFormat,
targetTextureWidth, targetTextureHeight, border,
format, type, data);
// set the filtering so we don't need mips
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
}
function degToRad(d) {
return d * Math.PI / 180;
}
var fieldOfViewRadians = degToRad(60);
var modelXRotationRadians = degToRad(0);
var modelYRotationRadians = degToRad(0);
// Get the starting time.
var then = 0;
requestAnimationFrame(drawScene);
function drawCube(aspect) {
// Tell it to use our program (pair of shaders)
gl.useProgram(program);
// Turn on the position attribute
gl.enableVertexAttribArray(positionLocation);
// Bind the position buffer.
gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
// Tell the position attribute how to get data out of positionBuffer (ARRAY_BUFFER)
var size = 3; // 3 components per iteration
var type = gl.FLOAT; // the data is 32bit floats
var normalize = false; // don't normalize the data
var stride = 0; // 0 = move forward size * sizeof(type) each iteration to get the next position
var offset = 0; // start at the beginning of the buffer
gl.vertexAttribPointer(
positionLocation, size, type, normalize, stride, offset);
// Turn on the teccord attribute
gl.enableVertexAttribArray(texcoordLocation);
// Bind the position buffer.
gl.bindBuffer(gl.ARRAY_BUFFER, texcoordBuffer);
// Tell the position attribute how to get data out of positionBuffer (ARRAY_BUFFER)
var size = 2; // 2 components per iteration
var type = gl.FLOAT; // the data is 32bit floats
var normalize = false; // don't normalize the data
var stride = 0; // 0 = move forward size * sizeof(type) each iteration to get the next position
var offset = 0; // start at the beginning of the buffer
gl.vertexAttribPointer(
texcoordLocation, size, type, normalize, stride, offset);
// Compute the projection matrix
var projectionMatrix =
m4.perspective(fieldOfViewRadians, aspect, 1, 2000);
var cameraPosition = [0, 0, 2];
var up = [0, 1, 0];
var target = [0, 0, 0];
// Compute the camera's matrix using look at.
var cameraMatrix = m4.lookAt(cameraPosition, target, up);
// Make a view matrix from the camera matrix.
var viewMatrix = m4.inverse(cameraMatrix);
var viewProjectionMatrix = m4.multiply(projectionMatrix, viewMatrix);
var matrix = m4.xRotate(viewProjectionMatrix, modelXRotationRadians);
matrix = m4.yRotate(matrix, modelYRotationRadians);
// Set the matrix.
gl.uniformMatrix4fv(matrixLocation, false, matrix);
// Tell the shader to use texture unit 0 for u_texture
gl.uniform1i(textureLocation, 0);
// Draw the geometry.
gl.drawArrays(gl.TRIANGLES, 0, 6 * 6);
}
// Draw the scene.
function drawScene(time) {
// convert to seconds
time *= 0.001;
// Subtract the previous time from the current time
var deltaTime = time - then;
// Remember the current time for the next frame.
then = time;
// Animate the rotation
modelYRotationRadians += -0.7 * deltaTime;
modelXRotationRadians += -0.4 * deltaTime;
webglUtils.resizeCanvasToDisplaySize(gl.canvas);
gl.enable(gl.CULL_FACE);
gl.enable(gl.DEPTH_TEST);
{
// render cube with our 3x2 texture
gl.bindTexture(gl.TEXTURE_2D, texture);
// Tell WebGL how to convert from clip space to pixels
gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);
// Clear the canvas AND the depth buffer.
gl.clearColor(0, 0, 1, 1); // clear to blue
gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
const aspect = targetTextureWidth / targetTextureHeight;
drawCube(aspect);
}
{
// render the cube with the texture we just rendered to
gl.bindTexture(gl.TEXTURE_2D, targetTexture);
gl.copyTexImage2D(
gl.TEXTURE_2D, //target
0, // mip level, has to be zero for default framebuffer
gl.RGBA, // pixel format, default framebuffer is RGBA
0, 0, // x,y
gl.drawingBufferWidth, // width
gl.drawingBufferHeight, // height
0 // border, always 0
);
// Tell WebGL how to convert from clip space to pixels
gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);
// Clear the canvas AND the depth buffer.
gl.clearColor(1, 1, 1, 1); // clear to white
gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
const aspect = gl.canvas.clientWidth / gl.canvas.clientHeight;
drawCube(aspect);
}
requestAnimationFrame(drawScene);
}
}
// Fill the buffer with the values that define a cube.
function setGeometry(gl) {
var positions = new Float32Array(
[
-0.5, -0.5, -0.5,
-0.5, 0.5, -0.5,
0.5, -0.5, -0.5,
-0.5, 0.5, -0.5,
0.5, 0.5, -0.5,
0.5, -0.5, -0.5,
-0.5, -0.5, 0.5,
0.5, -0.5, 0.5,
-0.5, 0.5, 0.5,
-0.5, 0.5, 0.5,
0.5, -0.5, 0.5,
0.5, 0.5, 0.5,
-0.5, 0.5, -0.5,
-0.5, 0.5, 0.5,
0.5, 0.5, -0.5,
-0.5, 0.5, 0.5,
0.5, 0.5, 0.5,
0.5, 0.5, -0.5,
-0.5, -0.5, -0.5,
0.5, -0.5, -0.5,
-0.5, -0.5, 0.5,
-0.5, -0.5, 0.5,
0.5, -0.5, -0.5,
0.5, -0.5, 0.5,
-0.5, -0.5, -0.5,
-0.5, -0.5, 0.5,
-0.5, 0.5, -0.5,
-0.5, -0.5, 0.5,
-0.5, 0.5, 0.5,
-0.5, 0.5, -0.5,
0.5, -0.5, -0.5,
0.5, 0.5, -0.5,
0.5, -0.5, 0.5,
0.5, -0.5, 0.5,
0.5, 0.5, -0.5,
0.5, 0.5, 0.5,
]);
gl.bufferData(gl.ARRAY_BUFFER, positions, gl.STATIC_DRAW);
}
// Fill the buffer with texture coordinates the cube.
function setTexcoords(gl) {
gl.bufferData(
gl.ARRAY_BUFFER,
new Float32Array(
[
0, 0,
0, 1,
1, 0,
0, 1,
1, 1,
1, 0,
0, 0,
0, 1,
1, 0,
1, 0,
0, 1,
1, 1,
0, 0,
0, 1,
1, 0,
0, 1,
1, 1,
1, 0,
0, 0,
0, 1,
1, 0,
1, 0,
0, 1,
1, 1,
0, 0,
0, 1,
1, 0,
0, 1,
1, 1,
1, 0,
0, 0,
0, 1,
1, 0,
1, 0,
0, 1,
1, 1,
]),
gl.STATIC_DRAW);
}
main();