glsl - Alpha-channel all 1.0 in WebGLRenderTarget when reading rendered image for post-processing -

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i using three.js render world webglrendertarget. world not full whole screen , thus, has transparent background. purpose provide alpha-channel aware image effects.

  1. i render world webglrendertarget buffer

  2. i try post-process reading buffer , writing real screen

my post-processing function depends on alpha channel. however, looks somehow three.js post-processing shader fails read alpha channel correctly - 1.0 no matter values try put in webglrendertarget.

the simple way demostrate problem.

i create render target:

        var rtparameters = { minfilter: three.linearfilter, magfilter: three.linearfilter, format: three.rgbaformat};          for(var i=0; i<this.buffercount; i++) {             this.buffers[i] = new three.webglrendertarget(this.width, this.height, rtparameters);         }

i clear buffer setting alpha 0.3::

        function clear(buf) {             // debugging purposes set clear color alpha             renderer.setclearcolor(new three.color(0xff00ff), 0.3);             renderer.cleartarget(buf, true, true, true);         }          // clean both buffers start         clear(buffers[0]);

and use buffer read buffer , render screen in post-processing fragment shader function (threejs post-processing examples):

            "void main() {",                      // texture buffer rendered before                     "vec4 sample = texture2d( texture, vuv);",                      // goes white (1.0) when trying visualize                     // alpha channel of rendered webgltarget.                     // should value 0.3 - slight gray                     "gl_fragcolor = vec4(sample.a, sample.a, sample.a, 1.0);",             "}"

other color values read correctly. if use vec4(sample.r, sample.g, sample.b, 1.0) directly copies expected.

  • is there problem of clearing alpha channel webglrendertarget?

  • is there problem of reading alpha values having webglrendertarget texture 2d image post-processing in glsl shader?

here fiddle implements believe trying achieve.

http://jsfiddle.net/6vk6w/3/


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