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improved precision of glReadPixels for colorbuffers < 24bpp

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This commit is contained in:
Brian Paul
2000-12-13 00:46:21 +00:00
parent 75639547e7
commit 062bc07bde
3 changed files with 74 additions and 6 deletions
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47
src/mesa/main/pixel.c
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@@ -1,4 +1,4 @@
/* $Id: pixel.c,v 1.20 2000/11/28 00:07:51 brianp Exp $ */
/* $Id: pixel.c,v 1.21 2000/12/13 00:46:21 brianp Exp $ */
/*
* Mesa 3-D graphics library
@@ -1109,3 +1109,48 @@ _mesa_map_stencil( const GLcontext *ctx, GLuint n, GLstencil stencil[] )
stencil[i] = ctx->Pixel.MapStoS[ stencil[i] & mask ];
}
}
/*
* This function converts an array of GLchan colors to GLfloat colors.
* Most importantly, it undoes the non-uniform quantization of pixel
* values introduced when we convert shallow (< 8 bit) pixel values
* to GLubytes in the ctx->Driver.ReadRGBASpan() functions.
* This fixes a number of OpenGL conformance failures when running on
* 16bpp displays, for example.
*/
void
_mesa_chan_to_float_span(const GLcontext *ctx, GLuint n,
CONST GLchan rgba[][4], GLfloat rgbaf[][4])
{
const GLuint rShift = CHAN_BITS - ctx->Visual.RedBits;
const GLuint gShift = CHAN_BITS - ctx->Visual.GreenBits;
const GLuint bShift = CHAN_BITS - ctx->Visual.BlueBits;
GLuint aShift;
const GLfloat rScale = 1.0 / (GLfloat) ((1 << ctx->Visual.RedBits ) - 1);
const GLfloat gScale = 1.0 / (GLfloat) ((1 << ctx->Visual.GreenBits) - 1);
const GLfloat bScale = 1.0 / (GLfloat) ((1 << ctx->Visual.BlueBits ) - 1);
GLfloat aScale;
GLuint i;
if (ctx->Visual.AlphaBits > 0) {
aShift = CHAN_BITS - ctx->Visual.AlphaBits;
aScale = 1.0 / (GLfloat) ((1 << ctx->Visual.AlphaBits) - 1);
}
else {
aShift = 0;
aScale = 1.0F / CHAN_MAXF;
}
for (i = 0; i < n; i++) {
const GLint r = rgba[i][RCOMP] >> rShift;
const GLint g = rgba[i][GCOMP] >> gShift;
const GLint b = rgba[i][BCOMP] >> bShift;
const GLint a = rgba[i][ACOMP] >> aShift;
rgbaf[i][RCOMP] = (GLfloat) r * rScale;
rgbaf[i][GCOMP] = (GLfloat) g * gScale;
rgbaf[i][BCOMP] = (GLfloat) b * bScale;
rgbaf[i][ACOMP] = (GLfloat) a * aScale;
}
}

7
src/mesa/main/pixel.h
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@@ -1,4 +1,4 @@
/* $Id: pixel.h,v 1.8 2000/11/28 00:07:51 brianp Exp $ */
/* $Id: pixel.h,v 1.9 2000/12/13 00:46:21 brianp Exp $ */
/*
* Mesa 3-D graphics library
@@ -131,4 +131,9 @@ extern void
_mesa_map_stencil(const GLcontext *ctx, GLuint n, GLstencil index[]);
extern void
_mesa_chan_to_float_span(const GLcontext *ctx, GLuint n,
CONST GLchan rgba[][4], GLfloat rgbaf[][4]);
#endif

26
src/mesa/swrast/s_readpix.c
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@@ -1,4 +1,4 @@
/* $Id: s_readpix.c,v 1.4 2000/11/28 00:04:39 brianp Exp $ */
/* $Id: s_readpix.c,v 1.5 2000/12/13 00:46:22 brianp Exp $ */
/*
* Mesa 3-D graphics library
@@ -716,9 +716,27 @@ static void read_rgba_pixels( GLcontext *ctx,
}
dst = _mesa_image_address(packing, pixels, width, height,
format, type, 0, row, 0);
_mesa_pack_rgba_span(ctx, readWidth, (const GLchan (*)[4]) rgba,
format, type, dst, packing,
ctx->_ImageTransferState);
if (ctx->Visual.RedBits < CHAN_BITS ||
ctx->Visual.GreenBits < CHAN_BITS ||
ctx->Visual.BlueBits < CHAN_BITS) {
/* Requantize the color values into floating point and go from
* there. This fixes conformance failures with 16-bit color
* buffers, for example.
*/
GLfloat rgbaf[MAX_WIDTH][4];
_mesa_chan_to_float_span(ctx, readWidth,
(CONST GLchan (*)[4]) rgba, rgbaf);
_mesa_pack_float_rgba_span(ctx, readWidth,
(CONST GLfloat (*)[4]) rgbaf,
format, type, dst, packing,
ctx->_ImageTransferState);
}
else {
/* GLubytes are fine */
_mesa_pack_rgba_span(ctx, readWidth, (CONST GLchan (*)[4]) rgba,
format, type, dst, packing,
ctx->_ImageTransferState);
}
}
}