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Open key color key / opengl

I need to implement a color function (removing a solid colored background) in an openFrameworks application.

I will play many (10 or more) videos at the same time (in the same frame) and draw them on the screen along with alternative backgrounds. I can achieve the effect characteristic of color, iterating through each pixel of the frame and setting alpha values ​​for each of them based on the green threshold, but with so many videos at once, this pixel offset becomes prohibitive.

Is there a simple OpenGL blending or masking mode that can avoid drawing all the pixels of a particular color value? Or is there another openFrameworks or openFrameworks-compatible C ++ library that can do this efficiently?

Alternatively, is there a good (space-efficient) way to store the alpha channel in QuickTime-compatible video files? We are going to store terabytes of video (weeks of continuous recording), so it is important that we use spatially efficient formats.

One note: the color color in the source files will be "perfect" - it is added digitally. Therefore, if there is some threshold or bitwise logical trick for this, this can also work.

EDIT : this is what worked following the VJo suggestion for a pixel shader. We used the glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)following pixel shader (for magenta as the replaced color):

"Data / Shaders / chromakey.frag":

#extension GL_ARB_texture_rectangle : enable

uniform sampler2DRect src_tex_unit0;
vec4 color;

void main( void )
{
        vec2 st = gl_TexCoord[0].st;
        vec4 sample = texture2DRect(src_tex_unit0, st );
        gl_FragColor = sample;
        if((sample.r > 0.5) && (sample.g < 0.5) && (sample.b > 0.5)) {
                gl_FragColor.a = 0.0;
        }
}

"Data / Shaders / chromakey.vert":

void main()
{
    gl_Position = ftransform();
    gl_TexCoord[0] = gl_MultiTexCoord[0];
}

C ++ proxy classes for shaders - shaderChromakey.h:

#include "ofMain.h"
#include "ofxShader.h"
#include "ofxFBOTexture.h"

class shaderChromakey{

    public:
        void setup(int fboW, int fboH);

        void beginRender();
        void endRender();

        void draw(int x, int y, int width, int height);

        ofxShader shader;

        ofxFBOTexture fbo;

};

shaderChromakey.cpp:

#include "shaderChromakey.h"

//--------------------------------------------------------------
void shaderChromakey::setup(int fboW, int fboH){ 

    ofBackground(255,255,255);
    ofSetVerticalSync(true);

    fbo.allocate(fboW, fboH, true);

    shader.loadShader("shaders/chromakey");
}

//--------------------------------------------------------------
void shaderChromakey::beginRender(){
    fbo.swapIn();
}

//--------------------------------------------------------------
void shaderChromakey::endRender(){
    fbo.swapOut();
}

//--------------------------------------------------------------
void shaderChromakey::draw(int x, int y, int width, int height){

    shader.setShaderActive(true);
    fbo.draw(x, y, width, height);
    shader.setShaderActive(false);
}

:

shaderChromakey chromakey;
chromakey.setup(HORIZONTAL, VERTICAL)

, :

chromakey.beginRender();
    // draw chomakeyed frame here
chromakey.endRender();
+5
1

glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_DST_ALPHA), , , , , , ( - 0).

+2

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