32-bit textures on 16-bit framebuffer

[muratmat]

I have an MBX lite chip mounted on a iMX31. Display is 16bpp, so window surfaces and context can be opened only in 565 (without alpha channel). If i create a 32bit texture with
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 128, 128, 0, GL_RGBA, GL_UNSIGNED_BYTE, pixels32) the driver seems to upload pixels inside its dedicated texture ram in a 4444 format, resulting (when the texture is used) in an ugly/low color block artifacts.

If i upload pixels in 5551 format, like this glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 128, 128, 0, GL_RGBA, GL_UNSIGNED_SHORT_5_5_5_1, pixels16) the driver seems to hold the pixels as they are, without downsampling they in an internal 4444 format like in the case above.

How can i make the OpenGL|ES driver use a full 32bit texture? i think that the screen format conversion must be done only when a pixel is going to be written, so if i use a 32bit texture, then a conversion to the framebuffer 565 format is done only in the final stage, not when texture is loaded...am i right?

In addition the driver seems to report an extension called GL_IMG_texture_format_BGRA8888, that seems not be documented. Is that extension the thing i miss to make the chip use internal 32bit textures/calculations? Can someone tell me how that extension can be used? Can someone tell me if it refers to an additional texture format (like for example GL_RGBA). In this case can someone give me the correct enumerated value correspoinding to that format?

Thanks in advance.

 

[Simon F]

How can i make the OpenGL|ES driver use a full 32bit texture? i think that the screen format conversion must be done only when a pixel is going to be written, so if i use a 32bit texture, then a conversion to the framebuffer 565 format is done only in the final stage, not when texture is loaded...am i right?

That is, indeed, what the hardware does.

Perhaps you could fire a question at the IMG/PowerVR development support team ?

 

[Rolf N]

Try using a sized internal format (third argument to your function call). GL_RGBA8 should give you what you want, and there's also GL_RGB5, GL_RGBA4, GL_RGB5_A1 etc. Note that this is not the same as the type and size arguments near the end of the argument list.

 

[Xmas]

Try using a sized internal format (third argument to your function call). GL_RGBA8 should give you what you want, and there's also GL_RGB5, GL_RGBA4, GL_RGB5_A1 etc. Note that this is not the same as the type and size arguments near the end of the argument list.

Those do not exist in OpenGL ES.

I've already answered on the Khronos message boards.