Conversion from BGRA to RGBA

[roccio]

Hello,
I have a byte array in BGRA format and I use it to update a sf::Texture. The problem is that sf::Texture only supports RGBA forrmat. Is there a fast solution for this conversion? Or (like I do now) I have to swap the bytes manually?

Thank you

[Laurent]

You can hack a faster solution with an OpenGL call:

sf::Texture::bind(&texture);
glTexSubImage2D(GL_TEXTURE_2D, 0, x, y, width, height, GL_BGRA, GL_UNSIGNED_BYTE, bytes);

Depending on how the driver implements the conversion, the speed difference may be more or less noticeable.

However this may break the internal cache of SFML. You can make it almost safe by preserving the texture binding:

GLint textureBinding;
glGetIntegerv(GL_TEXTURE_BINDING_2D, &textureBinding);
sf::Texture::bind(&texture);
glTexSubImage2D(GL_TEXTURE_2D, 0, x, y, width, height, GL_BGRA, GL_UNSIGNED_BYTE, bytes);
glBindTexture(GL_TEXTURE_2D, textureBinding);

Try with caution

[roccio]

I will try. Thank you Laurent!

[Aravol]

Looking at needing to do this exact thing for a current project. Would the rebind be necessary if the texture is only edited from a dedicated thread (ie only this thread edits this image, this thread only edits this image), or does the mentioned internal cache cross threads? If there's a difference, I'm also using the .NET wrappers rather than the C++ libraries.

[Laurent]

What's important is in which OpenGL context you perform the operation. If the thread uses the window's context (ie. you called window.SetActive(true) in the thread), then you need to preserve OpenGL states. If you're using a dedicated dummy context (ie. you instanciate the Context class at the beginning of your thread) then you don't have to do it.