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List:       mesa3d-dev
Subject:    [Mesa3d-dev] PRINT instruction for NV_vertex_program
From:       Brian Paul <brian.paul () tungstengraphics ! com>
Date:       2004-12-16 3:24:29
Message-ID: 41C0FFED.4090807 () tungstengraphics ! com
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I've been working through some vertex/fragment program bugs that I 
found recently, and as usual, I resorted to adding printf's in the 
Mesa code for vertex/fragment program execution in order to figure out 
what was going on.

It occured to me that I could add a 'print' instruction to the vertex 
program language to make things easer.  I just checked in the changes 
to do so.

Here's an example.  This is the vertex program from 
progs/demos/fplight.c with a PRINT instruction:

   "!!VP1.0\n"
   "# typical modelview/projection transform\n"
   "DP4   o[HPOS].x, c[0], v[OPOS] ;\n"
   "DP4   o[HPOS].y, c[1], v[OPOS] ;\n"
   "DP4   o[HPOS].z, c[2], v[OPOS] ;\n"
   "DP4   o[HPOS].w, c[3], v[OPOS] ;\n"
   "# transform normal by inv transpose of modelview, put in tex0\n"
   "DP3   o[TEX0].x, c[4], v[NRML] ;\n"
   "DP3   o[TEX0].y, c[5], v[NRML] ;\n"
   "DP3   o[TEX0].z, c[6], v[NRML] ;\n"
   "DP3   o[TEX0].w, c[7], v[NRML] ;\n"
   "PRINT 'texcoord = ', o[TEX0];\n"
   "END\n";

When the program is run you'd see this in stdout:

texcoord = 0, 0, 1, 15
texcoord = 0, 0, 1, 15
texcoord = 0, 0.587785, 0.809017, 12.1353
texcoord = -0.345492, 0.475528, 0.809017, 12.1353
texcoord = -0.559017, 0.181636, 0.809017, 12.1353
[...]


The PRINT instruction operands are a string literal inclosed in single 
quotes optionally followed by a register name.  It's really simple. 
There's no % substitutions like printf.

Of course, this probably isn't suitable for hardware execution but 
using software rendering for debugging can be better than nothing.

Eventually, I might also implement this in NV_fragment_program and 
ARB_vertex/fragment_program and make it into a real GL extension.

-Brian



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