javascript - WebGL 显示帧缓冲区？

Question

我使用了 WEBKIT_WEBGL_depth_texture 扩展。并初始化下面的缓冲区。但是我怎样才能绘制这个帧缓冲区呢？我现在完全被困住了。 -.-

function InitDepthtextures (){


var size = 256;

// Create a color texture
var colorTexture = gl.createTexture();
gl.bindTexture(gl.TEXTURE_2D, colorTexture);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_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);
gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, size, size, 0, gl.RGBA, gl.UNSIGNED_BYTE, null);

// Create the depth texture
depthTexture = gl.createTexture();
gl.bindTexture(gl.TEXTURE_2D, depthTexture);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_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);
gl.texImage2D(gl.TEXTURE_2D, 0, gl.DEPTH_COMPONENT, size, size, 0, gl.DEPTH_COMPONENT, gl.UNSIGNED_SHORT, null);

framebuffer = gl.createFramebuffer();
gl.bindFramebuffer(gl.FRAMEBUFFER, framebuffer);
gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, colorTexture, 0);
gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.DEPTH_ATTACHMENT, gl.TEXTURE_2D, depthTexture, 0);


//set to default
gl.bindTexture(gl.TEXTURE_2D, null);
gl.bindFramebuffer(gl.FRAMEBUFFER, null);

Answer 1

您不绘制帧缓冲区。你画纹理。因此，首先您将纹理附加到帧缓冲区。现在，在帧缓冲区绑定(bind)的情况下，绘制一些东西，结果被绘制到帧缓冲区的附件中。接下来取消绑定(bind)帧缓冲区并使用附加到帧缓冲区的纹理绘制一些东西以查看它们的内容。

例子:

const gl = document.querySelector('#c').getContext('webgl');

const vshader = `
    attribute vec4 a_position;
    varying vec2 v_texcoord;

    void main() {
      gl_Position = a_position;
      v_texcoord = a_position.xy * 0.5 + 0.5;
    }    
`;
const fshader = `
precision mediump float;
varying vec2 v_texcoord;
uniform sampler2D u_sampler;
void main() {
    gl_FragColor = texture2D(u_sampler, v_texcoord);
}
`;

// compiles shaders, links program
const program = twgl.createProgram(gl, [vshader, fshader]);
gl.useProgram(program);

const positionLocation = gl.getAttribLocation(program, "a_position");

// a single triangle from top right to bottom left to bottom right
const verts = [
      1,  1,
     -1,  1,
     -1, -1,
];   
const vertBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, vertBuffer);
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(verts), gl.STATIC_DRAW);
{
  const numElements = 2;
  const type = gl.FLOAT;
  const normalize = false;
  const stride = 0;
  const offset = 0;
  gl.vertexAttribPointer(
      positionLocation, numElements, type, normalize, stride, offset);
  gl.enableVertexAttribArray(positionLocation);
}

// create an empty texture
const tex = gl.createTexture();
gl.bindTexture(gl.TEXTURE_2D, tex);
{
  const level = 0;
  const internalFormat = gl.RGBA;
  const width = 1;
  const height = 1;
  const border = 0;
  const format = gl.RGBA;
  const type = gl.UNSIGNED_BYTE;
  const data = null;
  gl.texImage2D(gl.TEXTURE_2D, level, internalFormat, width, height, border,
                format, type, data);
}

// Create a framebuffer and attach the texture.
const fb = gl.createFramebuffer();
gl.bindFramebuffer(gl.FRAMEBUFFER, fb);
{
  const level = 0
  gl.framebufferTexture2D(
      gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, tex, level);
}

// Render to the texture (using clear because it's simple)
gl.clearColor(0, 1, 0, 1); // green;
gl.clear(gl.COLOR_BUFFER_BIT);

// Now draw with the texture to the canvas
// NOTE: We clear the canvas to red so we'll know
// so anywhere that shows up green is coming from the canvas texture
// from above.
gl.bindFramebuffer(gl.FRAMEBUFFER, null);
gl.clearColor(1, 0, 0, 1); // red
gl.clear(gl.COLOR_BUFFER_BIT);
{
  const offset = 0;
  const count = 3;
  gl.drawArrays(gl.TRIANGLES, offset, count);
}

canvas { border: 1px solid black; }

<script src="https://twgljs.org/dist/4.x/twgl.min.js"></script>
<canvas id="c" width="400" height="400"></canvas>

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