Contrast using Open GL ES

Hello All,

I am trying to do contrast on image using Open GL ES. following is code for contrast in the source code [sample from apple] regarding same. but seems like I am not getting desired output.

-(void) DoContrast:(float) aContrast
{
    GLfloat h = aContrast*0.5f;

    [EAGLContext setCurrentContext:context];

    glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);

    glActiveTexture(GL_TEXTURE0);
    glVertexPointer(2, GL_FLOAT, 0, spriteVertices);
    glEnableClientState(GL_VERTEX_ARRAY);
    glTexCoordPointer(2, GL_SHORT, 0, spriteTexcoords);
    glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE);
    glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB,      GL_MODULATE);
    glTexEnvi(GL_TEXTURE_ENV, GL_SRC0_RGB,         GL_TEXTURE);
    glTexEnvi(GL_TEXTURE_ENV, GL_SRC1_RGB,         GL_PRIMARY_COLOR);
    glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_ALPHA,    GL_REPLACE);
    glTexEnvi(GL_TEXTURE_ENV, GL_SRC0_ALPHA,       GL_TEXTURE);

    glActiveTexture(GL_TEXTURE1);
    glEnable(GL_TEXTURE_2D);
    glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE);
    glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB,      GL_ADD_SIGNED);
    glTexEnvi(GL_TEXTURE_ENV, GL_SRC0_RGB,         GL_PREVIOUS);
    glTexEnvi(GL_TEXTURE_ENV, GL_SRC1_RGB,         GL_PRIMARY_COLOR);
    glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_RGB,     GL_SRC_ALPHA);
    glTexEnvi(GL_TEXTURE_ENV, GL_RGB_SCALE,        2);
    glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_ALPHA,    GL_REPLACE);
    glTexEnvi(GL_TEXTURE_ENV, GL_SRC0_ALPHA,       GL_PREVIOUS);

    glColor4f(h, h, h, 0.75 - 0.5 * h); // 2x extrapolation
    validateTexEnv();
    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

    glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);

    [context presentRenderbuffer:GL_RENDERBUFFER_OES];

    glActiveTexture(GL_TEXTURE0);
    glDisable(GL_BLEND);
    glViewport(0, 0, backingWidth, backingHeight);

    [self drawView];
}

Can anyone help me if I am doing something wrong here.

thanks,

Sagar

ansaurus

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Contrast using Open GL ES

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