Size for IVideoDriver::createRenderTargetTexture()

[greenya]

Hello,

Documentation says:

Code: Select all

virtual ITexture* irr::video::IVideoDriver::createRenderTargetTexture( const core::dimension2d<s32> &size )

Creates a render target texture.

Parameters:
size,: Size of the texture, in pixels. Width and height should be a power of two (for example 64, 128, 256, 512, ...) and it should not be bigger than the backbuffer, because it shares the zbuffer with the screen buffer.

I guess the question is very stupid, but i want to know for sure, about "and it should not be bigger than the backbuffer":
If i have 800x600 mode what maximum size may i use ? (512x512 ?)
If i have 1024x768 mode --------------------------------- ? (1024x1024 or 1024x512 ?)

P.S.: How to determinate backbuffer size and check is this size acceptable?

[vitek]

How to determinate backbuffer size and check is this size acceptable?

You should be able to use driver->getScreenSize() to get the size of the back buffer.

If i have 800x600 mode what maximum size may i use ? (512x512 ?)

Yes.

If i have 1024x768 mode --------------------------------- ? (1024x1024 or 1024x512 ?)

1024x512

Code: Select all

core::dimension2d<s32>
getMaxRenderTargetSize(video::IVideoDriver* driver)
{
  const core::dimension2d<s32> ss = driver->getScreenSize();

  core::dimension2d<s32> result(1, 1);
  while (result.Width <= ss.Width)
    result.Width <<= 1;
  result.Width >>= 1;

  while (result.Height <= ss.Height)
    result.Height <<= 1;
  result.Height >>= 1;

  return result;
} 

[Luben]

Why is the max size that of the backbuffer? And why does dx force 2^n-sizes? Does this apply to all the drivers?

[hybrid]

The limitation to the backbuffer is because its zbuffer is reused, so you wouldn't get sane results otherwise. The Power-of-two is because no DirectX programmer in the team yet fixed it. It was reported that this limitation does not exists for D3D9, but I simply don't know and try to avoid messing with D3D stuff, and the others did not fix it. What about D3D8, is it also capable of NPOT RTT?

[LLDD]

I'm using rendertargets with the size of the backbuffer (non power of 2, like 640x480 etc) on the OpenGL driver and it works fine.
*edit* hybrid answered faster and better
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VAPORIZER AFFILIATE

[hybrid]

OpenGL supports this due to Framebuffer Objects.

[Luben]

Is the z-buffer also reused in opengl, or does the framebuffer object consist of all buffers needed to render?

[hybrid]

It contains all stuff so results are correct