如何告诉WebGL从屏幕中心进行渲染，然后以顺时针方向的块向外扩展，如果时间过长则取消/删除渲染？
还是我需要自己手动平铺多个画布，并在所有画布上进行投影？
答案 0 :(得分：1)
作为我对您的问题的评论的一个示例，这是一个过于简单的偏心渲染的示例。我以从this page渲染到纹理的示例开始。
那个
这个
有很多伪像，低分辨率纹理太低分辨率，您需要更好的算法在它们之间进行融合，但是可以显示效果。
唯一与众不同的事情
更改视口以仅渲染到中心。也可以通过缩放平面来做到这一点
// Tell WebGL how to convert from clip space to pixels
gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);
drawRenderTarget(lowResRT);
// Tell WebGL how to convert from clip space to pixels
gl.viewport(
gl.canvas.width / 4,
gl.canvas.height / 4,
gl.canvas.width / 2,
gl.canvas.height / 2);
drawRenderTarget(highResRT);
使用frustum函数来计算平截头体，而不是更传统的perspective函数。 frustum函数采用左，右，下，上，近，远参数，并计算投影矩阵，使眼睛在0、0处，左，右，上，下描述眼前的矩形。它比perspective函数更灵活，因为它允许消失点位于任何地方而不仅仅是中心。
在这种情况下，此代码计算视锥的正确值，视锥的中心在中间和近平面中，高度为2个单位，宽为2 *纵横比。相反，它计算一个子矩形。这就是我们使高分辨率纹理与低分辨率纹理匹配的方式
// Compute the projection matrix
var near = 1;
// compute a near plane 2 units tall, 2 * aspect high
var vTop = near * Math.tan(fieldOfViewRadians * 0.5);
var vHeight = 2 * vTop;
var vWidth = aspect * vHeight;
var vLeft = -0.5 * vWidth;
// how compute a subrect of that near plane where
// left, bottom are offsets into the computed near plane
// and width, height are the dimensions of the sub rect
vLeft += left * vWidth / 2;
vTop -= bottom * vHeight / 2;
vWidth *= width / 2;
vHeight *= height / 2;
var projectionMatrix =
m4.frustum(vLeft, vLeft + vWidth, vTop - vHeight, vTop, near, 2000);
"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 buffer for positions
var planePositionBuffer = gl.createBuffer();
// Bind it to ARRAY_BUFFER (think of it as ARRAY_BUFFER = positionBuffer)
gl.bindBuffer(gl.ARRAY_BUFFER, planePositionBuffer);
// Put the positions in the buffer
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([
-1, -1,
1, -1,
-1, 1,
-1, 1,
1, -1,
1, 1,
]), gl.STATIC_DRAW);
// provide texture coordinates for the rectangle.
var planeTexcoordBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, planeTexcoordBuffer);
// Set Texcoords.
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([
0, 0,
1, 0,
0, 1,
0, 1,
1, 0,
1, 1,
]), gl.STATIC_DRAW);
// Create a texture just for the cube.
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
function createRenderTarget(targetTextureWidth, targetTextureHeight) {
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);
}
// Create and bind the framebuffer
const fb = gl.createFramebuffer();
gl.bindFramebuffer(gl.FRAMEBUFFER, fb);
// attach the texture as the first color attachment
const attachmentPoint = gl.COLOR_ATTACHMENT0;
const level = 0;
gl.framebufferTexture2D(gl.FRAMEBUFFER, attachmentPoint, gl.TEXTURE_2D, targetTexture, level);
return {
framebuffer: fb,
texture: targetTexture,
width: targetTextureWidth,
height: targetTextureHeight,
};
}
const lowResRT = createRenderTarget(32, 32);
const highResRT = createRenderTarget(256, 256);
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, left, bottom, width, height) {
// 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 near = 1;
// compute a near plane 2 units tall, 2 * aspect high
var vTop = near * Math.tan(fieldOfViewRadians * 0.5);
var vHeight = 2 * vTop;
var vWidth = aspect * vHeight;
var vLeft = -0.5 * vWidth;
// how compute a subrect of that near plane where
// left, bottom are offsets into the computed near plane
// and width, height are the dimensions of the sub rect
vLeft += left * vWidth / 2;
vTop -= bottom * vHeight / 2;
vWidth *= width / 2;
vHeight *= height / 2;
var projectionMatrix =
m4.frustum(vLeft, vLeft + vWidth, vTop - vHeight, vTop, near, 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);
}
function drawPlane(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, planePositionBuffer);
// 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(
positionLocation, size, type, normalize, stride, offset);
// Turn on the teccord attribute
gl.enableVertexAttribArray(texcoordLocation);
// Bind the position buffer.
gl.bindBuffer(gl.ARRAY_BUFFER, planeTexcoordBuffer);
// 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 matrix = m4.identity();
// 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);
}
// 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);
function drawToRenderTarget(rt, left, bottom, width, height) {
// render to our targetTexture by binding the framebuffer
gl.bindFramebuffer(gl.FRAMEBUFFER, rt.framebuffer);
// render cube with our color texture
gl.bindTexture(gl.TEXTURE_2D, texture);
// Tell WebGL how to convert from clip space to pixels
gl.viewport(0, 0, rt.width, rt.height);
// Clear the attachment(s).
gl.clearColor(0, 0, 1, 1); // clear to blue
gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
const aspect = gl.canvas.clientWidth / gl.canvas.clientHeight;
drawCube(aspect, left, bottom, width, height);
}
drawToRenderTarget(lowResRT, 0, 0, 2, 2);
drawToRenderTarget(highResRT, 0.5, 0.5, 1, 1);
function drawRenderTarget(rt) {
// render to the canvas
gl.bindFramebuffer(gl.FRAMEBUFFER, null);
// render the cube with the texture we just rendered to
gl.bindTexture(gl.TEXTURE_2D, rt.texture);
const aspect = gl.canvas.clientWidth / gl.canvas.clientHeight;
drawPlane(aspect);
}
gl.disable(gl.DEPTH_TEST);
// Tell WebGL how to convert from clip space to pixels
gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);
drawRenderTarget(lowResRT);
// Tell WebGL how to convert from clip space to pixels
gl.viewport(
gl.canvas.width / 4,
gl.canvas.height / 4,
gl.canvas.width / 2,
gl.canvas.height / 2);
drawRenderTarget(highResRT);
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();body {
margin: 0;
}
canvas {
width: 100vw;
height: 100vh;
display: block;
}<canvas id="canvas"></canvas>
<!-- vertex shader -->
<script id="3d-vertex-shader" type="x-shader/x-vertex">
attribute vec4 a_position;
attribute vec2 a_texcoord;
uniform mat4 u_matrix;
varying vec2 v_texcoord;
void main() {
// Multiply the position by the matrix.
gl_Position = u_matrix * a_position;
// Pass the texcoord to the fragment shader.
v_texcoord = a_texcoord;
}
</script>
<!-- fragment shader -->
<script id="3d-fragment-shader" type="x-shader/x-fragment">
precision mediump float;
// Passed in from the vertex shader.
varying vec2 v_texcoord;
// The texture.
uniform sampler2D u_texture;
void main() {
gl_FragColor = texture2D(u_texture, v_texcoord);
}
</script><!--
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