R300 To Do list
And here is the R300 to do list (at the end of this page); if you feel something is missing please add it. If you have done something and it no longer needs to be investigated, happily erase it from here :).
Hardware limitations
Should this be its own page? Probably not.
Some of these are errata, some aren't. You can't work around them in hardware, though.
- Vertex shader limits
ALU
Const
Temp
Alt.Temp
R300
256
256
32
20
R400
256
256
32
20
R500
1024
256
32
20
- Fragment shader limits
ALU
TEX
Const
Temp
Samplers
TEX Indirections
R300
64
32
32
32
16
4
R400
512
512
32
64
16
4
R500
512
512
256
128
16
Unlimited
- Shader opcodes (unlisted opcodes are not supported)
R300 VS
R500 VS
R300 FS
R500 FS
ABS
Source operand modifier
ADD
ARL
ARR
CND
src0 > 0.5 ? src1 : src2
can be used for e.g. src0 ? src1 : src2
CMP
src0 < 0.0 ? src1 : src2
COS
DDX
DDY
DP2A
DP3
DP4
DST
EX2
EXP
FRC
KIL
LG2
LIT
LOG
MAD
MAX
MIN
MUL
POW
RCP
RSQ
SEQ
SGE
SGT
SIN
SLT
SNE
*_SAT
Instruction modififer
TEX
TXB
TXD
TXL
TXP
IF
ELSE
ENDIF
BGNLOOP
There are a lot of restrictions on loops.
BRK
CONT
ENDLOOP
- Geometry
- Vertex formats GL_*INT and GL_DOUBLE are not supported. GL_*SHORT is supported only for 2- and 4-component vertex attributes, and GL_*BYTE only for 4-component attributes. All individual vertex attribute fetches must be DWORD-aligned.
- Quads and quadstrips cannot have the first vertex be the provoking vertex.
- Rasterizer
- The interpolated colors have a range of [0, 1] and are limited to 12 bits of precision. Unlike texture coordinates, when multisampling is enabled, the colors are sampled at the centroid of the covered portion of the fragment. With PS3 mode enabled (GUESS), the interpolated colors have 32 bits of precision.
- Textures
- Floating-point mipmap LOD clamping is not supported. Min LOD is floor'd and max LOD is ceil'd.
- NPOT textures are not available, just rectangle textures (with possibility of normalized texture coordinates and bilinear filtering).
- Floating-point textures cannot be filtered, the only allowed filter modes are GL_NEAREST and GL_NEAREST_MIPMAP_NEAREST.
- Floating-point textures cannot be used with the wrap modes GL_CLAMP and GL_CLAMP_TO_BORDER, except for R500, which does support these modes.
- 16-bits-per-channel textures cannot be used with the wrap modes GL_CLAMP and GL_CLAMP_TO_BORDER.
- Vertex shader
- Vertex shaders evaluate 0^0 as NaN.
- Fragment shader
- Fragment derivatives are calculated at half resolution.
- R300 fragment shaders evaluate 0^0 as NaN.
- Color buffers
- R300 maximum color buffer size is 2560x2560. R400 maximum color buffer size is 4021x4021. R500 maximum color buffer size is 4096x4096
- R300-R400 cannot do blending, alpha-testing, and multisampling with floating-point colorbuffers. R500 can do these only for GL_RGBA16F.
Gallium3D Driver
This is a TODO list for r300g.
- Driver enhancements
- Add MSAA (multisampled polys) and Alpha-To-Coverage (multisampled alpha-tested edges), centroid GLSL varying modifier.
- Add texture-stuffing-based things: smoothed points + lines + polygons, and stippled lines + polygons. This needs changes in the rasterizer, the RS block, and the fragment shading.
- Fix and enable Hyper-Z by default (probably on r500 only due to lack of testing coverage).
- Compiler enhancements
- Improve the VS register allocator to be more useful with ifs and loops (We should be able to reuse most of the FS register allocator for this).
- VS: Implement Dual-Op Vector/Math (4D+1D) instruction pair scheduling. Performance++.
- State tracker enhancements
- Implement accelerated pixel buffer objects (we can do the aligned copies at least).
Implement accelerated CopyBufferSubData.
- Bugs
- Fix piglit tests.