Hi,
Um, please ignore the 1st suggestion; it was already in Mesa and I was not
awake of enough. Sighs.
________________________________
From: Rogovin, Kevin
Sent: Monday, February 10, 2014 12:06 PM
To: mesa-dev@lists.freedesktop.org
Cc: Romanick, Ian D
Subject: Texture from RenderBuffer for blitting
Hi,
I was looking over the _mesa_meta_BlitFramebuffer and in particular,
blitframebuffer_texture(). A few idea (feedback welcome and wanted):
Firstly, the check if src is a renderbuffer or not. I think it might be a good
idea to add an internal Mesa API to allow a driver to specify that a
renderbuffer can be used as a texture. I believe that atleast for i965, this
would make that blitframebuffer_texture() would likely always be used when i965
blitframebuffer implementation uses _mesa_meta_BlitFramebuffer.
Secondly, if a driver supports MRT, I think it would be better to use an MRT
fragment shader instead of a looping over each render target. Indeed, by doing
so, the read associated to the texture fetch would happen once instead of once
per color buffer.
Thirdly (and this is quite minor), rather than using a VBO to hold the vertex
data, I'd think it would be better if the vertex data was static values {
{0,1}, {1,0}, {1,1}, {0,1} } and the vertex shader would have uniforms that
takes the local normalized values and produces the texture coordinate (and clip
positional values). The reason being that since the same buffer object is used,
changing it and then using it means that if an application does several blits
in a row then an underlying driver will either stall or do "something" for the
buffer object (for i965 since it is small, this means copy it usually).
Lastly, in handling the case where the src and dest are the same buffers in the
case where the buffer can be viewed as a texture rather than using
CopyTex[Sub]Image to a temporary buffer, to instead use
blitframebuffer_texture() onto a temporary texture and then use
blitframebuffer_texture() onto the dest. The main benefit being that various
format conversion cases are then handled properly (since CopyTex[Sub]Image
requires the formats to match more closely than BlitFramebuffer requires).
-Kevin
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