Hi,
    I'd like to blend 2 images together such that I can control how much of
each image is output. However, I need to vary the proportion of each image
that is used throughout the image. For example, the top-left part of the
resultant image might contain contributions from the 2 input images in the
proportion of say 10/90%, whilst the bottom left might contain contributions
in the proportions 50/50%. I'd like to be able to control the per pixel
contribution proporting using a single 8-bit plane, where each value would
define the proportion (unless there's a better way of doing it?).

Is this 'do-able' in OpenGL in a way that might support a decent (say 30f/s)
frame rate?. Also, has anybody any ideas on appropriate/efficient mechanisms
that would provide such behaviour?.

Ta,.
Dave

Dave Moore wrote:
> Hi,
>     I'd like to blend 2 images together such that I can control how much of
> each image is output. However, I need to vary the proportion of each image
> that is used throughout the image. For example, the top-left part of the
> resultant image might contain contributions from the 2 input images in the
> proportion of say 10/90%, whilst the bottom left might contain contributions
> in the proportions 50/50%. I'd like to be able to control the per pixel
> contribution proporting using a single 8-bit plane, where each value would
> define the proportion (unless there's a better way of doing it?).
> 
> Is this 'do-able' in OpenGL in a way that might support a decent (say 30f/s)
> frame rate?.

Of course!

> Also, has anybody any ideas on appropriate/efficient mechanisms
> that would provide such behaviour?.
> 

You need to but your 8-bit blending info into a texture.
Now you use multitexturing, put your blending info into
texture 1 and image A into texture 2 and draw a quad
using glBlendFunc(GL_SRC_ALPHA, GL_ZERO). This puts
image A in the frame buffer.

Now do the same with image B but change the blending
to (GL_ONE_MINUS_SRC_ALPHA, GL_ONE). This adds image B
to the framebuffer.

If you can use fragment shaders then you can do it all
in one pass.


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