| Summary: | r600g: Sampling from an alpha texture in a fragment shader | ||
|---|---|---|---|
| Product: | Mesa | Reporter: | Owen Taylor <otaylor> |
| Component: | Drivers/Gallium/r600 | Assignee: | Default DRI bug account <dri-devel> |
| Status: | RESOLVED FIXED | QA Contact: | |
| Severity: | normal | ||
| Priority: | medium | ||
| Version: | git | ||
| Hardware: | Other | ||
| OS: | All | ||
| Whiteboard: | |||
| i915 platform: | i915 features: | ||
| Attachments: |
piglit patch described
Slightly simpler version of Piglit test |
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Created attachment 40449 [details] [review] Slightly simpler version of Piglit test Here's a slightly simpler version of the test (gets rid of multiplying by a color) I'm a little reluctant to provide any of the results of my experiments trying to understand this, since I'm still confused and maybe will just confuse anybody following on, but in the SQ_TEX_WORD1 generated from: 0: TEX TEMP[0], IN[0], SAMP[0], 2D If I manually tweak the DST_SEL_X/DEST_SEL_Y/DEST_SEL_Z/DEST_SEL_W I see the following results for the loaded stored into the temporary: Sel Result xyzw xyzw --------- 1000 1000 0100 0100 0010 0010 0001 0001 0w00 0000 0w01 0001 100w 1001 1w00 1100 (example A) w000 w000 w001 w001 ww01 ww01 (example B) w100 w100 w00w w00w So, in the marked example A above, if I set DST_SEL_X to SQ_SEL_1 and DST_SEL_Y to SQ_SEL_W and DST_SEL_Z and DST_SEL_W to SQ_SEL_0, then I end up with a value that has 1's for x and y, and 0's for z and w. Possibly wrong interpretation: In all the cases above what you an observe is that the value of a component is the same as if you first replaced w with the value selected by DST_SEL_X and then applied the actual selector. So, DST_SEL_Y=SQ_SEL_W in example A gave us 1 because DST_SEL_X=SQ_SEL_1, but in example B it gave us w because DST_SEL_X=SQ_SEL_1. This might have something to do with the interaction with the swizzle inherent to the A8 texture format that sets X,Y,Z=0 and W=X. That would match up with this only occurring for A8 textures and not for RGBA textures. but I don't understand why a swizzle at texture load time would cause the selectors from INST_TEX to have a double effect. Anyways, I'm still confused. I don't really have time to work on this more, but if it isn't obvious, then one possible approach would be to compare the bytecode and texture setup of the classic driver (which works for this) to what the gallium driver is doing. Oh, and I should mention that I did my testing on an RV710, in case it's a r6xx/r7xx difference. just FYI for anyone else looking at this: its something to do with the staged texture upload code. disabling it makes it all a lot happier should be fixed by d5aadf0d80e8c973ef5cf9d82e97f23f0e3c032b in mesa master. Thanks Owen for the test program made it a lot easier to track down. |
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Created attachment 40447 [details] piglit patch described The attach piglit addition works on g600c and softpipe fails on r600g. (The test is close to minimal, but not having diagnosed the bug I don't know if "sampling from an alpha texture" is the fundamental thing that needs to be tested or not... or there could even be failing piglit tests elsewhere that are showing the same problem.) The TGSI looks right: DCL IN[0], COLOR, LINEAR DCL IN[1], GENERIC[0], PERSPECTIVE DCL OUT[0], COLOR DCL SAMP[0] DCL TEMP[0] 0: TEX TEMP[0], IN[1], SAMP[0], 2D 1: MUL OUT[0], IN[0], TEMP[0].wwww 2: END VERT Despite spending a lot of time fooling around this yesterday and checking what I thought were the obvious things I really have no idea what is going on; hopefully it will be obvious for someone more familiar with the R700 shader code.