Set transparent color in RGB image

Graphics and GPU Programming Programming OpenGL

Started by lyen February 28, 2010 08:10 PM

4 comments, last by V-man 14 years, 1 month ago

100

Author

February 28, 2010 08:10 PM

I am new to OpenGL ES, hopefully someone could kindly help me out. I have a RGB image with pink color set as transparency color. While in Direct3D, we can easily set the modulate color while creating the texture, my question is, how do we set up a transparency modulate color in OpenGL ES? In another word, how can I tell the graphic unit not to draw pink color when it's processing the texture. Thanks in advance.

Juanxo

189

February 28, 2010 08:19 PM

Hi lyen!

I haven't used OpenGL ES, but IMO, it's easier to apply the alpha layer in any graphics program (like Phothoshop), and save the image as png.

lyen

100

Author

March 01, 2010 02:02 AM

Thanks for the reply and your suggestion, Juanxo.

I know what you suggested is a viable solution, but the programmer in me would like to know if there is a solution to programatically handle such issue =).

karwosts

841

March 01, 2010 02:22 AM

I don't think OpenGL has a function for this (possibly some obscure extension that I don't know of though).

To do this you can either use a shader, or loop through the texture on CPU replacing pink with alpha before uploading.

The latter is probably the best idea as its a one time hit, and the branching required to implement this in a shader may not be very efficient.

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lyen

100

Author

March 01, 2010 01:16 PM

After a day of research, looks like Karwosts' suggestion is the most feasible.

DirectX does this for programmer during texture creation, I think OpenGL just wants us work a bit harder =).

Thanks all for your suggestions and help!

V-man

813

March 01, 2010 02:59 PM

Quote:Original post by lyen
After a day of research, looks like Karwosts' suggestion is the most feasible.

DirectX does this for programmer during texture creation, I think OpenGL just wants us work a bit harder =).

Thanks all for your suggestions and help!

You are thinking of D3DX, the utility library.
The equivalent of the D3DX are some libraries at the Alternative Game Lib forum
here on gamedev.
A lot of stuff for doing math, quaternion, image manipulation.
Perhaps DevIL do what you want (DevIL = Developer Image Library)

Sig: http://glhlib.sourceforge.net
an open source GLU replacement library. Much more modern than GLU.
float matrix[16], inverse_matrix[16];
glhLoadIdentityf2(matrix);
glhTranslatef2(matrix, 0.0, 0.0, 5.0);
glhRotateAboutXf2(matrix, angleInRadians);
glhScalef2(matrix, 1.0, 1.0, -1.0);
glhQuickInvertMatrixf2(matrix, inverse_matrix);
glUniformMatrix4fv(uniformLocation1, 1, FALSE, matrix);
glUniformMatrix4fv(uniformLocation2, 1, FALSE, inverse_matrix);

Set transparent color in RGB image

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Set transparent color in RGB image

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