[Bug 43191] Radeons needs 2D (MACRO) color tiling for optimal performance

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=43191

--- Comment #3 from Simon Farnsworth <simon.farnsworth at onelan.co.uk> 2011-11-23 11:07:44 PST ---
Created attachment 53817
  --> https://bugs.freedesktop.org/attachment.cgi?id=53817
A program to draw red/green rectangles using raw X11. Compile as gcc -o
rectangle rectangle.c -lX11

I've started trying to analyze what's going on, using the attached program - my
next step is going to be working out how to get at the scanout buffer directly.

I'm running this program against an otherwise unused (no other clients) X
server, started as:

Xorg :0 -noreset -nolisten tcp vt1

and set to low resolution with:

xrandr --output DisplayPort-0 --mode 640x480

In the meantime, I have the following unexpected result: When I run the
attached program as "./rectangle 16 1 1 1", which should give me one red pixel
above one green pixel, 16 pixels from the left edge of the screen, I see 4
pixels light up. It *looks* like I get the 2 pixels I expect, plus a pair at 8
pixels in, 16 pixels down.

I have also determined that I see the same unexpected pair light up if I run it
as "./rectangle 0 17 1 1", requesting 0 pixels offset, 17 pixels wide, and 1
pixel height of each colour. Final oddity is that "./rectangle 0 16 2 1" gives
me two lines of 16 wide red pixels, no green, while "./rectangle 0 16 1 2"
gives me one line 16 wide red, one line 16 wide green.

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