equivalent of gl.readBuffer(gl.COLOR_ATTACHMENTx) in webgl 1.0

问题

i need to render to 2 textures (in on pass of course)

var extbuffers = gl.getExtension('WEBGL_draw_buffers');

var tex1 = gl.createTexture();  
//gl.activeTexture(gl.TEXTURE1);  
gl.bindTexture(gl.TEXTURE_2D, tex1);  
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);
gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, PVS, PVS, 0, gl.RGBA,gl.FLOAT,null);


var tex2 = gl.createTexture();
//gl.activeTexture(gl.TEXTURE2);  
gl.bindTexture(gl.TEXTURE_2D, tex2);
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);
gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, PVS, PVS, 0, gl.RGBA, gl.FLOAT, null);  



gl.bindFramebuffer(gl.FRAMEBUFFER, gl.createFramebuffer());
gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, tex1, 0);  

gl.framebufferTexture2D(gl.FRAMEBUFFER, extbuffers.COLOR_ATTACHMENT1_WEBGL, gl.TEXTURE_2D, tex2, 0);

extbuffers.drawBuffersWEBGL(
// Here, we give it the list of slots we want to draw to.
[
    extbuffers.COLOR_ATTACHMENT0_WEBGL, // gl_FragData[0]
    extbuffers.COLOR_ATTACHMENT1_WEBGL  // gl_FragData[1]
]
);

and the fragment shader :

#extension GL_EXT_draw_buffers : require

void main() {

                gl_FragData[0] = vec4(pos,vit);
                gl_FragData[1] = vec4(col,1.0);
}

but now is my problem : how can i read the textures ? I have readen some similar questions but about FramebufferRenderbuffer

i would like a :

gl.readBuffer(gl.COLOR_ATTACHMENT0);
gl.readPixels(...);

gl.readBuffer(gl.COLOR_ATTACHMENT1);
gl.readPixels(...);

Thanks.

EDIT : i use Webgl 1, but with ad hoc extension WEBGL_draw_buffers

回答1:

Create more framebuffers, attach the textures individually to those framebuffers, bind those framebuffers when you want to read from the textures.

Effectively

create texture1
create texture2

create drawFramebuffer
   attach texture1 as color attachment0
   attach texture2 as color attachment1

create readFramebuffer1
   attach texture1 as color attachment0

create readFramebuffer2
   attach texture2 as color attachment0

Now you bind drawFramebuffer when you want to draw, bind readFrambuffer1 when you want to read from texture1 and bind readFrameubffer2 when you want to read from texture2

来源：https://stackoverflow.com/questions/52427194/equivalent-of-gl-readbuffergl-color-attachmentx-in-webgl-1-0

标签

WebGL