如何快速翻转 OpenGL ES FBO？

Question

version:Android OpenGL ES 2.0

I use 5 filters and FBO to render a bitmap, every filter need bitmap texture and bitmap's mask texture, my problem is after every filter render, the next filter get FBO is upside-down, mask and texture orientation are opposite on even-numbered filter,I want to know how to fast flip FBO before next filter use it?

#version 100
precision mediump float;
uniform sampler2D uTexture;
uniform sampler2D uMaskTexture;
varying vec2 vTexCoord;
void main(){
    float mask=texture2D(uMaskTexture, vTexCoord);
    gl_FragColor=texture2D(uTexture*mask, vTexCoord);
}

To simplify the problem, the 5 filters are similar to the code above. uTexture comes from the FBO of the previous filter and uMaskTexture is a texture without any changes

Answer 1

It seems that your texture coordinates are wrong. Correct the texture coordinate attribute. This means that you have to "flip" the y component of the texture coordinate. 0 becomes 1 and 1 becomes 0:

Of course this also can be done in the fragment shader:

void main()
{
    vec2 uv = vec2(vTexCoord.x, 1.0-vTexCoord.y);
    float mask = texture2D(uMaskTexture, uv);
    gl_FragColor = texture2D(uTexture, uv) * mask;
}

or in the vertex shader:

attribute vec2 aTexCoord;

varying vec2 vTexCoord;

void main
{
    vTexCoord = vec2(aTexCoord.x, 1.0-aTexCoord.y);

    // [...]
}