First off, I'm experiencing this on WinXP/Radeon9800SE/1.4.4145. The problem doesn't appear on MacOSX/Radeon9800Pro. Don't have access to NVIDIA boards.

Here's the gist. The VP addresses xy-offsets for billboards with an ARL instruction. Initially it worked fine, but with minor changes to the VP, the xy-offset appears to be stuck at 0. But in the latter case, there appears to be a workaround whereby multiplying the xy-offset by 1 kicks the value back to what it should be. Now for some details...

In the code below, the 4 xy-offsets (one for each corner of a billboard) are passed via the `spriteOffsets' param. Each vertex stores its "corner ID" in the `corner.x' attrib (vertex.attrib[9]), which is used to define the address register `arOffset' with an ARL instruction. The initial version of the VP (which worked fine) used spriteOffsets[arOffset.x] directly in an arithmetic instruction. Among other details, the salient change appears to be that the value of spriteOffsets[arOffset.x] is now copied (MOV) to a temp, `xyoffset'.

In debugging the problem, I first noticed that multiplying xyoffset by a constant had no effect, but if I masked the dest register with `.xy', it all worked. So the following line seems to work around the problem:

MUL xyoffset.xy, xyoffset, 1;

Any thoughts, insights, or similar experiences?

Here's the complete VP:

--------------------------------------------

!!ARBvp1.0

PARAM animationAlpha = program.local[0];

PARAM zoffset = program.local[1];

PARAM spriteOffsets[4] = { program.local[2..5] };

PARAM defaultColor = program.local[6];

PARAM sizeModulation = program.local[7];

PARAM mvp[4] = { state.matrix.mvp };

PARAM zero = { 0, 0, 0, 1 };

ATTRIB corner = vertex.attrib[9];

TEMP centerPos, cornerPos, nodeSize, color, texcoord, xyoffset;

ADDRESS arOffset;

DP4 centerPos.x, mvp[0], vertex.position;

DP4 centerPos.y, mvp[1], vertex.position;

DP4 centerPos.z, mvp[2], vertex.position;

DP4 centerPos.w, mvp[3], vertex.position;

ARL arOffset.x, corner.x;

MOV xyoffset, spriteOffsets[arOffset.x];

MUL xyoffset.xy, xyoffset, 1; # workaround for bug on WinXP/Radeon9800

MOV nodeSize, 1;

MOV nodeSize.xy, vertex.attrib[10].x;

# nodeSize = sizeModulation * nodeSize + 1 - sizeModulation;

# cornerPos = nodeSize * xyoffset + centerPos;

# result.position = cornerPos + zoffset;

MAD nodeSize.xy, sizeModulation.x, nodeSize, 1;

ADD nodeSize.xy, nodeSize, -sizeModulation.x;

MAD cornerPos, nodeSize, xyoffset, centerPos;

ADD result.position, cornerPos, zoffset;

MUL color, defaultColor, vertex.color;

MUL color.w, color, animationAlpha;

MOV result.color, color;

MOV texcoord, zero;

MOV texcoord.xy, vertex.texcoord[0];

MOV result.texcoord[0], texcoord;

END