diff options
Diffstat (limited to 'src/mesa/swrast')
| -rw-r--r-- | src/mesa/swrast/s_tritemp.h | 80 |
1 files changed, 51 insertions, 29 deletions
diff --git a/src/mesa/swrast/s_tritemp.h b/src/mesa/swrast/s_tritemp.h index 1949e7cd40f..74dc13e2997 100644 --- a/src/mesa/swrast/s_tritemp.h +++ b/src/mesa/swrast/s_tritemp.h @@ -1,8 +1,8 @@ /* * Mesa 3-D graphics library - * Version: 5.1 + * Version: 6.1 * - * Copyright (C) 1999-2003 Brian Paul All Rights Reserved. + * Copyright (C) 1999-2004 Brian Paul All Rights Reserved. * * Permission is hereby granted, free of charge, to any person obtaining a * copy of this software and associated documentation files (the "Software"), @@ -63,6 +63,34 @@ * This code was designed for the origin to be in the lower-left corner. * * Inspired by triangle rasterizer code written by Allen Akin. Thanks Allen! + * + * + * Some notes on rasterization accuracy: + * + * This code uses fixed point arithmetic (the GLfixed type) to iterate + * over the triangle edges and interpolate ancillary data (such as Z, + * color, secondary color, etc). The number of fractional bits in + * GLfixed and the value of SUB_PIXEL_BITS has a direct bearing on the + * accuracy of rasterization. + * + * If SUB_PIXEL_BITS=4 then we'll snap the vertices to the nearest + * 1/16 of a pixel. If we're walking up a long, nearly vertical edge + * (dx=1/16, dy=1024) we'll need 4 + 10 = 14 fractional bits in + * GLfixed to walk the edge without error. If the maximum viewport + * height is 4K pixels, then we'll need 4 + 12 = 16 fractional bits. + * + * Historically, Mesa has used 11 fractional bits in GLfixed, snaps + * vertices to 1/16 pixel and allowed a maximum viewport height of 2K + * pixels. 11 fractional bits is actually insufficient for accurately + * rasterizing some triangles. More recently, the maximum viewport + * height was increased to 4K pixels. Thus, Mesa should be using 16 + * fractional bits in GLfixed. Unfortunately, there may be some issues + * with setting FIXED_FRAC_BITS=16, such as multiplication overflow. + * This will have to be examined in some detail... + * + * For now, if you find rasterization errors, particularly with tall, + * sliver triangles, try increasing FIXED_FRAC_BITS and/or decreasing + * SUB_PIXEL_BITS. */ @@ -558,24 +586,18 @@ static void NAME(GLcontext *ctx, const SWvertex *v0, */ { - int subTriangle; - GLfixed fx; + GLint subTriangle; GLfixed fxLeftEdge = 0, fxRightEdge = 0; GLfixed fdxLeftEdge = 0, fdxRightEdge = 0; - GLfixed fdxOuter; - int idxOuter; - float dxOuter; GLfixed fError = 0, fdError = 0; - float adjx, adjy; - GLfixed fy; #ifdef PIXEL_ADDRESS PIXEL_TYPE *pRow = NULL; - int dPRowOuter = 0, dPRowInner; /* offset in bytes */ + GLint dPRowOuter = 0, dPRowInner; /* offset in bytes */ #endif #ifdef INTERP_Z # ifdef DEPTH_TYPE DEPTH_TYPE *zRow = NULL; - int dZRowOuter = 0, dZRowInner; /* offset in bytes */ + GLint dZRowOuter = 0, dZRowInner; /* offset in bytes */ # endif GLfixed zLeft = 0, fdzOuter = 0, fdzInner; #endif @@ -659,31 +681,31 @@ static void NAME(GLcontext *ctx, const SWvertex *v0, } if (setupLeft && eLeft->lines > 0) { - const SWvertex *vLower; - GLfixed fsx = eLeft->fsx; - fx = FixedCeil(fsx); + const SWvertex *vLower = eLeft->v0; + const GLfixed fsx = eLeft->fsx; /* no fractional part */ + const GLfixed fsy = eLeft->fsy; + const GLfixed fx = FixedCeil(fsx); /* no fractional part */ + const GLfloat adjx = (GLfloat) (fx - eLeft->fx0); /* SCALED! */ + const GLfloat adjy = eLeft->adjy; /* SCALED! */ + GLfixed fdxOuter; + GLint idxOuter; + GLfloat dxOuter; + fError = fx - fsx - FIXED_ONE; fxLeftEdge = fsx - FIXED_EPSILON; fdxLeftEdge = eLeft->fdxdy; fdxOuter = FixedFloor(fdxLeftEdge - FIXED_EPSILON); fdError = fdxOuter - fdxLeftEdge + FIXED_ONE; idxOuter = FixedToInt(fdxOuter); - dxOuter = (float) idxOuter; - (void) dxOuter; + dxOuter = (GLfloat) idxOuter; - fy = eLeft->fsy; - span.y = FixedToInt(fy); + span.y = FixedToInt(fsy); - adjx = (float)(fx - eLeft->fx0); /* SCALED! */ - adjy = eLeft->adjy; /* SCALED! */ -#ifndef __IBMCPP__ - (void) adjx; /* silence compiler warnings */ - (void) adjy; /* silence compiler warnings */ -#endif - vLower = eLeft->v0; -#ifndef __IBMCPP__ - (void) vLower; /* silence compiler warnings */ -#endif + /* silence warnings on some compilers */ + (void) dxOuter; + (void) adjx; + (void) adjy; + (void) vLower; #ifdef PIXEL_ADDRESS { @@ -694,7 +716,7 @@ static void NAME(GLcontext *ctx, const SWvertex *v0, #endif /* * Now we need the set of parameter (z, color, etc.) values at - * the point (fx, fy). This gives us properly-sampled parameter + * the point (fx, fsy). This gives us properly-sampled parameter * values that we can step from pixel to pixel. Furthermore, * although we might have intermediate results that overflow * the normal parameter range when we step temporarily outside |