Bug 106074

Summary:	radv: si_scissor_from_viewport returns incorrect result when using half-pixel viewport offset
Product:	Mesa	Reporter:	Philip Rebohle <philip.rebohle>
Component:	Drivers/Vulkan/radeon	Assignee:	mesa-dev
Status:	RESOLVED FIXED	QA Contact:	mesa-dev
Severity:	normal
Priority:	medium	CC:	fdsfgs, gloriouseggroll
Version:	git
Hardware:	Other
OS:	All
Whiteboard:
i915 platform:		i915 features:
Attachments:	Sample program to demonstrate the issue Proposed patch

Description Philip Rebohle 2018-04-16 11:35:40 UTC

Created attachment 138865 [details]
Sample program to demonstrate the issue

For the following viewport, si_scissor_from_viewport returns an incorrect scissor rectangle:

  VkViewport vp = { 0.5f, 1.5f, 1.0f, -1.0f, 0.0f, 1.0f };

Expected result:  offset = (0,0), size = (1,1)
Actual result:    offset = (1,1), size = (0,0)

This breaks Final Fantasy XIV on DXVK, see:
https://github.com/doitsujin/dxvk/issues/208

The attachment contains a small C program to demonstrate the issue with the relevant functions directly taken from si_cmd_buffer.c.

Comment 1 Philip Rebohle 2018-04-16 14:52:08 UTC

Created attachment 138867 [details] [review]
Proposed patch

The attached patch fixes the issue in FF XIV. I'm not sure if that is entirely correct, but the use of the integer version of 'abs' in the following code looks incorrect given that 'scale[i]' can be non-integer even if the viewport size is integer.

    rect.offset.x = translate[0] - abs(scale[0]);
    rect.offset.y = translate[1] - abs(scale[1]);
    rect.extent.width = ceilf(translate[0] + abs(scale[0])) - rect.offset.x;
    rect.extent.height = ceilf(translate[1] + abs(scale[1])) - rect.offset.y;

Also it seems that my assumption that the size should be (1,1) was incorrect, it should indeed be (2,2). This is in line with what RadeonSI returns.

Comment 2 Samuel Pitoiset 2018-04-17 20:13:21 UTC

I have pushed your patch, thanks!

https://cgit.freedesktop.org/mesa/mesa/commit/?id=893e19efb74edd6133a607e09338bf5d449632f1

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