GLImageProcessing Multiple Filters?

Question

I have read through this question here: Can example "GLImageProcessing" work with multi filters However, I still do not understand how to edit the sample code fo

Answer 1

I was able to combine multiple filters and here is complete method based on the suggestions made here.

void drawGL(int wide, int high, float val, int mode)
{

    static int prevmode = -1;
    typedef void (*procfunc)(V2fT2f *, float);

    typedef struct {
            procfunc func;
            procfunc degen;
    } Filter;

    const Filter filter[] = {
            { brightness             },
            { contrast               },
            { extrapolate, greyscale },
            { hue                    },
            { extrapolate, blur      },        // The blur could be exaggerated by downsampling to half size
    };
    #define NUM_FILTERS (sizeof(filter)/sizeof(filter[0]))
    rt_assert(mode < NUM_FILTERS);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrthof(0, wide, 0, high, -1, 1);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glScalef(wide, high, 1);

glGetIntegerv(GL_FRAMEBUFFER_BINDING_OES, (GLint *)&SystemFBO);
// Create the texture and the FBO the will hold the result of applying the first filter
glGenTextures(1, &ResultTexture.texID);
glBindTexture(GL_TEXTURE_2D, ResultTexture.texID);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, wide, high, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glGenFramebuffersOES(1, &ResultTextureFBO);
glBindFramebufferOES(GL_FRAMEBUFFER_OES, ResultTextureFBO);
glFramebufferTexture2DOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_TEXTURE_2D, ResultTexture.texID, 0);

glBindFramebufferOES(GL_FRAMEBUFFER_OES, ResultTextureFBO);
glBindTexture(GL_TEXTURE_2D, Input.texID);

    glViewport(0, 0, wide, high);
brightness(flipquad, val);
    glCheckError();

glBindFramebufferOES(GL_FRAMEBUFFER_OES, SystemFBO);
glBindTexture(GL_TEXTURE_2D, ResultTexture.texID);

    glViewport(0, 0, wide, high);
hue(fullquad, val);
    glCheckError();    
}