need some help on bgfx::blit

[WKJingtian]

this is a code snippet where I used bgfx::blit:

textureHandle tex = createTexture2D(width, height, false, 1, bgfx::TextureFormat::RGBA8,BGFX_TEXTURE_READ_BACK | BGFX_TEXTURE_BLIT_DST);
bgfx::touch(A_VIEW_NEVER_USED);
bgfx::blit(A_VIEW_NEVER_USED, tex , 0, 0, bgfx::getTexture(A_FRAMEBUFFER), 0, 0, width, height);

the texture I obtained from this process was pure black (if read it, it's just 0x00), which was not how the frame buffer looked like.
Did I miss anything?

[bkaradzic]

which was not how the frame buffer looked like.

• How it looked like?
• Which renderer?
• Which platform?

[WKJingtian]

blit takes more than one frame too? If I use READ_BACK flag to create the DST texture but do not call readTexture() on it, shouldn't blit still happen in the same frame?

[WKJingtian]

I did some more tests on my own code and example 8.
If I use either BGFX_TEXTURE_READ_BACK or BGFX_TEXTURE_READ_BACK | BGFX_TEXTURE_BLIT_DST, I can get a valid result from bgfx::readTexture(). But if I bind this texture and show it on screen, it is just pure black.
I guess the read back flag prevents the texture from showing up on screen?
But anyway, I just want to save the texture as an image so using BGFX_TEXTURE_READ_BACK is the correct answer for me. Thanks!

[bkaradzic]

But if I bind this texture and show it on screen, it is just pure black.

You can't sample BGFX_TEXTURE_READ_BACK texture because it's CPU only texture.

[WKJingtian]

I see! thanks a lot for the explanation

[bkaradzic]

I added validation to catch when you set BGFX_TEXTURE_READ_BACK as texture to be sampled: 2d9e6e7