2 * Mesa 3-D graphics library
4 * Copyright (C) 1999-2007 Brian Paul All Rights Reserved.
6 * Permission is hereby granted, free of charge, to any person obtaining a
7 * copy of this software and associated documentation files (the "Software"),
8 * to deal in the Software without restriction, including without limitation
9 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
10 * and/or sell copies of the Software, and to permit persons to whom the
11 * Software is furnished to do so, subject to the following conditions:
13 * The above copyright notice and this permission notice shall be included
14 * in all copies or substantial portions of the Software.
16 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
17 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
19 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
20 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
21 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
22 * OTHER DEALINGS IN THE SOFTWARE.
26 * Triangle Rasterizer Template
28 * This file is #include'd to generate custom triangle rasterizers.
30 * The following macros may be defined to indicate what auxillary information
31 * must be interpolated across the triangle:
32 * INTERP_Z - if defined, interpolate integer Z values
33 * INTERP_RGB - if defined, interpolate integer RGB values
34 * INTERP_ALPHA - if defined, interpolate integer Alpha values
35 * INTERP_INT_TEX - if defined, interpolate integer ST texcoords
36 * (fast, simple 2-D texture mapping, without
37 * perspective correction)
38 * INTERP_ATTRIBS - if defined, interpolate arbitrary attribs (texcoords,
39 * varying vars, etc) This also causes W to be
40 * computed for perspective correction).
42 * When one can directly address pixels in the color buffer the following
43 * macros can be defined and used to compute pixel addresses during
44 * rasterization (see pRow):
45 * PIXEL_TYPE - the datatype of a pixel (GLubyte, GLushort, GLuint)
46 * BYTES_PER_ROW - number of bytes per row in the color buffer
47 * PIXEL_ADDRESS(X,Y) - returns the address of pixel at (X,Y) where
48 * Y==0 at bottom of screen and increases upward.
50 * Similarly, for direct depth buffer access, this type is used for depth
51 * buffer addressing (see zRow):
52 * DEPTH_TYPE - either GLushort or GLuint
54 * Optionally, one may provide one-time setup code per triangle:
55 * SETUP_CODE - code which is to be executed once per triangle
57 * The following macro MUST be defined:
58 * RENDER_SPAN(span) - code to write a span of pixels.
60 * This code was designed for the origin to be in the lower-left corner.
62 * Inspired by triangle rasterizer code written by Allen Akin. Thanks Allen!
65 * Some notes on rasterization accuracy:
67 * This code uses fixed point arithmetic (the GLfixed type) to iterate
68 * over the triangle edges and interpolate ancillary data (such as Z,
69 * color, secondary color, etc). The number of fractional bits in
70 * GLfixed and the value of SUB_PIXEL_BITS has a direct bearing on the
71 * accuracy of rasterization.
73 * If SUB_PIXEL_BITS=4 then we'll snap the vertices to the nearest
74 * 1/16 of a pixel. If we're walking up a long, nearly vertical edge
75 * (dx=1/16, dy=1024) we'll need 4 + 10 = 14 fractional bits in
76 * GLfixed to walk the edge without error. If the maximum viewport
77 * height is 4K pixels, then we'll need 4 + 12 = 16 fractional bits.
79 * Historically, Mesa has used 11 fractional bits in GLfixed, snaps
80 * vertices to 1/16 pixel and allowed a maximum viewport height of 2K
81 * pixels. 11 fractional bits is actually insufficient for accurately
82 * rasterizing some triangles. More recently, the maximum viewport
83 * height was increased to 4K pixels. Thus, Mesa should be using 16
84 * fractional bits in GLfixed. Unfortunately, there may be some issues
85 * with setting FIXED_FRAC_BITS=16, such as multiplication overflow.
86 * This will have to be examined in some detail...
88 * For now, if you find rasterization errors, particularly with tall,
89 * sliver triangles, try increasing FIXED_FRAC_BITS and/or decreasing
95 #define MAX_GLUINT 0xffffffff
100 * Some code we unfortunately need to prevent negative interpolated colors.
102 #ifndef CLAMP_INTERPOLANT
103 #define CLAMP_INTERPOLANT(CHANNEL, CHANNELSTEP, LEN) \
105 GLfixed endVal = span.CHANNEL + (LEN) * span.CHANNELSTEP; \
107 span.CHANNEL -= endVal; \
109 if (span.CHANNEL < 0) { \
116 static void NAME(struct gl_context
*ctx
, const SWvertex
*v0
,
121 const SWvertex
*v0
, *v1
; /* Y(v0) < Y(v1) */
122 GLfloat dx
; /* X(v1) - X(v0) */
123 GLfloat dy
; /* Y(v1) - Y(v0) */
124 GLfloat dxdy
; /* dx/dy */
125 GLfixed fdxdy
; /* dx/dy in fixed-point */
126 GLfloat adjy
; /* adjust from v[0]->fy to fsy, scaled */
127 GLfixed fsx
; /* first sample point x coord */
129 GLfixed fx0
; /* fixed pt X of lower endpoint */
130 GLint lines
; /* number of lines to be sampled on this edge */
133 const SWcontext
*swrast
= SWRAST_CONTEXT(ctx
);
135 const GLint depthBits
= ctx
->DrawBuffer
->Visual
.depthBits
;
136 const GLint fixedToDepthShift
= depthBits
<= 16 ? FIXED_SHIFT
: 0;
137 const GLfloat maxDepth
= ctx
->DrawBuffer
->_DepthMaxF
;
138 #define FixedToDepth(F) ((F) >> fixedToDepthShift)
140 EdgeT eMaj
, eTop
, eBot
;
142 const SWvertex
*vMin
, *vMid
, *vMax
; /* Y(vMin)<=Y(vMid)<=Y(vMax) */
143 GLfloat bf
= SWRAST_CONTEXT(ctx
)->_BackfaceSign
;
144 const GLint snapMask
= ~((FIXED_ONE
/ (1 << SUB_PIXEL_BITS
)) - 1); /* for x/y coord snapping */
145 GLfixed vMin_fx
, vMin_fy
, vMid_fx
, vMid_fy
, vMax_fx
, vMax_fy
;
151 INIT_SPAN(span
, GL_POLYGON
);
152 span
.y
= 0; /* silence warnings */
155 (void) fixedToDepthShift
;
159 printf("%s()\n", __FUNCTION__);
160 printf(" %g, %g, %g\n",
161 v0->attrib[VARYING_SLOT_POS][0],
162 v0->attrib[VARYING_SLOT_POS][1],
163 v0->attrib[VARYING_SLOT_POS][2]);
164 printf(" %g, %g, %g\n",
165 v1->attrib[VARYING_SLOT_POS][0],
166 v1->attrib[VARYING_SLOT_POS][1],
167 v1->attrib[VARYING_SLOT_POS][2]);
168 printf(" %g, %g, %g\n",
169 v2->attrib[VARYING_SLOT_POS][0],
170 v2->attrib[VARYING_SLOT_POS][1],
171 v2->attrib[VARYING_SLOT_POS][2]);
174 /* Compute fixed point x,y coords w/ half-pixel offsets and snapping.
175 * And find the order of the 3 vertices along the Y axis.
178 const GLfixed fy0
= FloatToFixed(v0
->attrib
[VARYING_SLOT_POS
][1] - 0.5F
) & snapMask
;
179 const GLfixed fy1
= FloatToFixed(v1
->attrib
[VARYING_SLOT_POS
][1] - 0.5F
) & snapMask
;
180 const GLfixed fy2
= FloatToFixed(v2
->attrib
[VARYING_SLOT_POS
][1] - 0.5F
) & snapMask
;
184 vMin
= v0
; vMid
= v1
; vMax
= v2
;
185 vMin_fy
= fy0
; vMid_fy
= fy1
; vMax_fy
= fy2
;
187 else if (fy2
<= fy0
) {
189 vMin
= v2
; vMid
= v0
; vMax
= v1
;
190 vMin_fy
= fy2
; vMid_fy
= fy0
; vMax_fy
= fy1
;
194 vMin
= v0
; vMid
= v2
; vMax
= v1
;
195 vMin_fy
= fy0
; vMid_fy
= fy2
; vMax_fy
= fy1
;
202 vMin
= v1
; vMid
= v0
; vMax
= v2
;
203 vMin_fy
= fy1
; vMid_fy
= fy0
; vMax_fy
= fy2
;
206 else if (fy2
<= fy1
) {
208 vMin
= v2
; vMid
= v1
; vMax
= v0
;
209 vMin_fy
= fy2
; vMid_fy
= fy1
; vMax_fy
= fy0
;
214 vMin
= v1
; vMid
= v2
; vMax
= v0
;
215 vMin_fy
= fy1
; vMid_fy
= fy2
; vMax_fy
= fy0
;
219 /* fixed point X coords */
220 vMin_fx
= FloatToFixed(vMin
->attrib
[VARYING_SLOT_POS
][0] + 0.5F
) & snapMask
;
221 vMid_fx
= FloatToFixed(vMid
->attrib
[VARYING_SLOT_POS
][0] + 0.5F
) & snapMask
;
222 vMax_fx
= FloatToFixed(vMax
->attrib
[VARYING_SLOT_POS
][0] + 0.5F
) & snapMask
;
225 /* vertex/edge relationship */
226 eMaj
.v0
= vMin
; eMaj
.v1
= vMax
; /*TODO: .v1's not needed */
227 eTop
.v0
= vMid
; eTop
.v1
= vMax
;
228 eBot
.v0
= vMin
; eBot
.v1
= vMid
;
230 /* compute deltas for each edge: vertex[upper] - vertex[lower] */
231 eMaj
.dx
= FixedToFloat(vMax_fx
- vMin_fx
);
232 eMaj
.dy
= FixedToFloat(vMax_fy
- vMin_fy
);
233 eTop
.dx
= FixedToFloat(vMax_fx
- vMid_fx
);
234 eTop
.dy
= FixedToFloat(vMax_fy
- vMid_fy
);
235 eBot
.dx
= FixedToFloat(vMid_fx
- vMin_fx
);
236 eBot
.dy
= FixedToFloat(vMid_fy
- vMin_fy
);
238 /* compute area, oneOverArea and perform backface culling */
240 const GLfloat area
= eMaj
.dx
* eBot
.dy
- eBot
.dx
* eMaj
.dy
;
242 if (IS_INF_OR_NAN(area
) || area
== 0.0F
)
245 if (area
* bf
* swrast
->_BackfaceCullSign
< 0.0)
248 oneOverArea
= 1.0F
/ area
;
250 /* 0 = front, 1 = back */
251 span
.facing
= oneOverArea
* bf
> 0.0F
;
254 /* Edge setup. For a triangle strip these could be reused... */
256 eMaj
.fsy
= FixedCeil(vMin_fy
);
257 eMaj
.lines
= FixedToInt(FixedCeil(vMax_fy
- eMaj
.fsy
));
258 if (eMaj
.lines
> 0) {
259 eMaj
.dxdy
= eMaj
.dx
/ eMaj
.dy
;
260 eMaj
.fdxdy
= SignedFloatToFixed(eMaj
.dxdy
);
261 eMaj
.adjy
= (GLfloat
) (eMaj
.fsy
- vMin_fy
); /* SCALED! */
263 eMaj
.fsx
= eMaj
.fx0
+ (GLfixed
) (eMaj
.adjy
* eMaj
.dxdy
);
269 eTop
.fsy
= FixedCeil(vMid_fy
);
270 eTop
.lines
= FixedToInt(FixedCeil(vMax_fy
- eTop
.fsy
));
271 if (eTop
.lines
> 0) {
272 eTop
.dxdy
= eTop
.dx
/ eTop
.dy
;
273 eTop
.fdxdy
= SignedFloatToFixed(eTop
.dxdy
);
274 eTop
.adjy
= (GLfloat
) (eTop
.fsy
- vMid_fy
); /* SCALED! */
276 eTop
.fsx
= eTop
.fx0
+ (GLfixed
) (eTop
.adjy
* eTop
.dxdy
);
279 eBot
.fsy
= FixedCeil(vMin_fy
);
280 eBot
.lines
= FixedToInt(FixedCeil(vMid_fy
- eBot
.fsy
));
281 if (eBot
.lines
> 0) {
282 eBot
.dxdy
= eBot
.dx
/ eBot
.dy
;
283 eBot
.fdxdy
= SignedFloatToFixed(eBot
.dxdy
);
284 eBot
.adjy
= (GLfloat
) (eBot
.fsy
- vMin_fy
); /* SCALED! */
286 eBot
.fsx
= eBot
.fx0
+ (GLfixed
) (eBot
.adjy
* eBot
.dxdy
);
291 * Conceptually, we view a triangle as two subtriangles
292 * separated by a perfectly horizontal line. The edge that is
293 * intersected by this line is one with maximal absolute dy; we
294 * call it a ``major'' edge. The other two edges are the
295 * ``top'' edge (for the upper subtriangle) and the ``bottom''
296 * edge (for the lower subtriangle). If either of these two
297 * edges is horizontal or very close to horizontal, the
298 * corresponding subtriangle might cover zero sample points;
299 * we take care to handle such cases, for performance as well
302 * By stepping rasterization parameters along the major edge,
303 * we can avoid recomputing them at the discontinuity where
304 * the top and bottom edges meet. However, this forces us to
305 * be able to scan both left-to-right and right-to-left.
306 * Also, we must determine whether the major edge is at the
307 * left or right side of the triangle. We do this by
308 * computing the magnitude of the cross-product of the major
309 * and top edges. Since this magnitude depends on the sine of
310 * the angle between the two edges, its sign tells us whether
311 * we turn to the left or to the right when travelling along
312 * the major edge to the top edge, and from this we infer
313 * whether the major edge is on the left or the right.
315 * Serendipitously, this cross-product magnitude is also a
316 * value we need to compute the iteration parameter
317 * derivatives for the triangle, and it can be used to perform
318 * backface culling because its sign tells us whether the
319 * triangle is clockwise or counterclockwise. In this code we
320 * refer to it as ``area'' because it's also proportional to
321 * the pixel area of the triangle.
325 GLint scan_from_left_to_right
; /* true if scanning left-to-right */
328 * Execute user-supplied setup code
334 scan_from_left_to_right
= (oneOverArea
< 0.0F
);
337 /* compute d?/dx and d?/dy derivatives */
339 span
.interpMask
|= SPAN_Z
;
341 GLfloat eMaj_dz
= vMax
->attrib
[VARYING_SLOT_POS
][2] - vMin
->attrib
[VARYING_SLOT_POS
][2];
342 GLfloat eBot_dz
= vMid
->attrib
[VARYING_SLOT_POS
][2] - vMin
->attrib
[VARYING_SLOT_POS
][2];
343 span
.attrStepX
[VARYING_SLOT_POS
][2] = oneOverArea
* (eMaj_dz
* eBot
.dy
- eMaj
.dy
* eBot_dz
);
344 if (span
.attrStepX
[VARYING_SLOT_POS
][2] > maxDepth
||
345 span
.attrStepX
[VARYING_SLOT_POS
][2] < -maxDepth
) {
346 /* probably a sliver triangle */
347 span
.attrStepX
[VARYING_SLOT_POS
][2] = 0.0;
348 span
.attrStepY
[VARYING_SLOT_POS
][2] = 0.0;
351 span
.attrStepY
[VARYING_SLOT_POS
][2] = oneOverArea
* (eMaj
.dx
* eBot_dz
- eMaj_dz
* eBot
.dx
);
354 span
.zStep
= SignedFloatToFixed(span
.attrStepX
[VARYING_SLOT_POS
][2]);
356 span
.zStep
= (GLint
) span
.attrStepX
[VARYING_SLOT_POS
][2];
360 span
.interpMask
|= SPAN_RGBA
;
361 if (ctx
->Light
.ShadeModel
== GL_SMOOTH
) {
362 GLfloat eMaj_dr
= (GLfloat
) (vMax
->color
[RCOMP
] - vMin
->color
[RCOMP
]);
363 GLfloat eBot_dr
= (GLfloat
) (vMid
->color
[RCOMP
] - vMin
->color
[RCOMP
]);
364 GLfloat eMaj_dg
= (GLfloat
) (vMax
->color
[GCOMP
] - vMin
->color
[GCOMP
]);
365 GLfloat eBot_dg
= (GLfloat
) (vMid
->color
[GCOMP
] - vMin
->color
[GCOMP
]);
366 GLfloat eMaj_db
= (GLfloat
) (vMax
->color
[BCOMP
] - vMin
->color
[BCOMP
]);
367 GLfloat eBot_db
= (GLfloat
) (vMid
->color
[BCOMP
] - vMin
->color
[BCOMP
]);
369 GLfloat eMaj_da
= (GLfloat
) (vMax
->color
[ACOMP
] - vMin
->color
[ACOMP
]);
370 GLfloat eBot_da
= (GLfloat
) (vMid
->color
[ACOMP
] - vMin
->color
[ACOMP
]);
372 span
.attrStepX
[VARYING_SLOT_COL0
][0] = oneOverArea
* (eMaj_dr
* eBot
.dy
- eMaj
.dy
* eBot_dr
);
373 span
.attrStepY
[VARYING_SLOT_COL0
][0] = oneOverArea
* (eMaj
.dx
* eBot_dr
- eMaj_dr
* eBot
.dx
);
374 span
.attrStepX
[VARYING_SLOT_COL0
][1] = oneOverArea
* (eMaj_dg
* eBot
.dy
- eMaj
.dy
* eBot_dg
);
375 span
.attrStepY
[VARYING_SLOT_COL0
][1] = oneOverArea
* (eMaj
.dx
* eBot_dg
- eMaj_dg
* eBot
.dx
);
376 span
.attrStepX
[VARYING_SLOT_COL0
][2] = oneOverArea
* (eMaj_db
* eBot
.dy
- eMaj
.dy
* eBot_db
);
377 span
.attrStepY
[VARYING_SLOT_COL0
][2] = oneOverArea
* (eMaj
.dx
* eBot_db
- eMaj_db
* eBot
.dx
);
378 span
.redStep
= SignedFloatToFixed(span
.attrStepX
[VARYING_SLOT_COL0
][0]);
379 span
.greenStep
= SignedFloatToFixed(span
.attrStepX
[VARYING_SLOT_COL0
][1]);
380 span
.blueStep
= SignedFloatToFixed(span
.attrStepX
[VARYING_SLOT_COL0
][2]);
382 span
.attrStepX
[VARYING_SLOT_COL0
][3] = oneOverArea
* (eMaj_da
* eBot
.dy
- eMaj
.dy
* eBot_da
);
383 span
.attrStepY
[VARYING_SLOT_COL0
][3] = oneOverArea
* (eMaj
.dx
* eBot_da
- eMaj_da
* eBot
.dx
);
384 span
.alphaStep
= SignedFloatToFixed(span
.attrStepX
[VARYING_SLOT_COL0
][3]);
385 # endif /* INTERP_ALPHA */
388 assert(ctx
->Light
.ShadeModel
== GL_FLAT
);
389 span
.interpMask
|= SPAN_FLAT
;
390 span
.attrStepX
[VARYING_SLOT_COL0
][0] = span
.attrStepY
[VARYING_SLOT_COL0
][0] = 0.0F
;
391 span
.attrStepX
[VARYING_SLOT_COL0
][1] = span
.attrStepY
[VARYING_SLOT_COL0
][1] = 0.0F
;
392 span
.attrStepX
[VARYING_SLOT_COL0
][2] = span
.attrStepY
[VARYING_SLOT_COL0
][2] = 0.0F
;
397 span
.attrStepX
[VARYING_SLOT_COL0
][3] = span
.attrStepY
[VARYING_SLOT_COL0
][3] = 0.0F
;
401 #endif /* INTERP_RGB */
402 #ifdef INTERP_INT_TEX
404 GLfloat eMaj_ds
= (vMax
->attrib
[VARYING_SLOT_TEX0
][0] - vMin
->attrib
[VARYING_SLOT_TEX0
][0]) * S_SCALE
;
405 GLfloat eBot_ds
= (vMid
->attrib
[VARYING_SLOT_TEX0
][0] - vMin
->attrib
[VARYING_SLOT_TEX0
][0]) * S_SCALE
;
406 GLfloat eMaj_dt
= (vMax
->attrib
[VARYING_SLOT_TEX0
][1] - vMin
->attrib
[VARYING_SLOT_TEX0
][1]) * T_SCALE
;
407 GLfloat eBot_dt
= (vMid
->attrib
[VARYING_SLOT_TEX0
][1] - vMin
->attrib
[VARYING_SLOT_TEX0
][1]) * T_SCALE
;
408 span
.attrStepX
[VARYING_SLOT_TEX0
][0] = oneOverArea
* (eMaj_ds
* eBot
.dy
- eMaj
.dy
* eBot_ds
);
409 span
.attrStepY
[VARYING_SLOT_TEX0
][0] = oneOverArea
* (eMaj
.dx
* eBot_ds
- eMaj_ds
* eBot
.dx
);
410 span
.attrStepX
[VARYING_SLOT_TEX0
][1] = oneOverArea
* (eMaj_dt
* eBot
.dy
- eMaj
.dy
* eBot_dt
);
411 span
.attrStepY
[VARYING_SLOT_TEX0
][1] = oneOverArea
* (eMaj
.dx
* eBot_dt
- eMaj_dt
* eBot
.dx
);
412 span
.intTexStep
[0] = SignedFloatToFixed(span
.attrStepX
[VARYING_SLOT_TEX0
][0]);
413 span
.intTexStep
[1] = SignedFloatToFixed(span
.attrStepX
[VARYING_SLOT_TEX0
][1]);
416 #ifdef INTERP_ATTRIBS
418 /* attrib[VARYING_SLOT_POS][3] is 1/W */
419 const GLfloat wMax
= vMax
->attrib
[VARYING_SLOT_POS
][3];
420 const GLfloat wMin
= vMin
->attrib
[VARYING_SLOT_POS
][3];
421 const GLfloat wMid
= vMid
->attrib
[VARYING_SLOT_POS
][3];
423 const GLfloat eMaj_dw
= wMax
- wMin
;
424 const GLfloat eBot_dw
= wMid
- wMin
;
425 span
.attrStepX
[VARYING_SLOT_POS
][3] = oneOverArea
* (eMaj_dw
* eBot
.dy
- eMaj
.dy
* eBot_dw
);
426 span
.attrStepY
[VARYING_SLOT_POS
][3] = oneOverArea
* (eMaj
.dx
* eBot_dw
- eMaj_dw
* eBot
.dx
);
429 if (swrast
->_InterpMode
[attr
] == GL_FLAT
) {
430 ASSIGN_4V(span
.attrStepX
[attr
], 0.0, 0.0, 0.0, 0.0);
431 ASSIGN_4V(span
.attrStepY
[attr
], 0.0, 0.0, 0.0, 0.0);
435 for (c
= 0; c
< 4; c
++) {
436 GLfloat eMaj_da
= vMax
->attrib
[attr
][c
] * wMax
- vMin
->attrib
[attr
][c
] * wMin
;
437 GLfloat eBot_da
= vMid
->attrib
[attr
][c
] * wMid
- vMin
->attrib
[attr
][c
] * wMin
;
438 span
.attrStepX
[attr
][c
] = oneOverArea
* (eMaj_da
* eBot
.dy
- eMaj
.dy
* eBot_da
);
439 span
.attrStepY
[attr
][c
] = oneOverArea
* (eMaj
.dx
* eBot_da
- eMaj_da
* eBot
.dx
);
447 * We always sample at pixel centers. However, we avoid
448 * explicit half-pixel offsets in this code by incorporating
449 * the proper offset in each of x and y during the
450 * transformation to window coordinates.
452 * We also apply the usual rasterization rules to prevent
453 * cracks and overlaps. A pixel is considered inside a
454 * subtriangle if it meets all of four conditions: it is on or
455 * to the right of the left edge, strictly to the left of the
456 * right edge, on or below the top edge, and strictly above
457 * the bottom edge. (Some edges may be degenerate.)
459 * The following discussion assumes left-to-right scanning
460 * (that is, the major edge is on the left); the right-to-left
461 * case is a straightforward variation.
463 * We start by finding the half-integral y coordinate that is
464 * at or below the top of the triangle. This gives us the
465 * first scan line that could possibly contain pixels that are
466 * inside the triangle.
468 * Next we creep down the major edge until we reach that y,
469 * and compute the corresponding x coordinate on the edge.
470 * Then we find the half-integral x that lies on or just
471 * inside the edge. This is the first pixel that might lie in
472 * the interior of the triangle. (We won't know for sure
473 * until we check the other edges.)
475 * As we rasterize the triangle, we'll step down the major
476 * edge. For each step in y, we'll move an integer number
477 * of steps in x. There are two possible x step sizes, which
478 * we'll call the ``inner'' step (guaranteed to land on the
479 * edge or inside it) and the ``outer'' step (guaranteed to
480 * land on the edge or outside it). The inner and outer steps
481 * differ by one. During rasterization we maintain an error
482 * term that indicates our distance from the true edge, and
483 * select either the inner step or the outer step, whichever
484 * gets us to the first pixel that falls inside the triangle.
486 * All parameters (z, red, etc.) as well as the buffer
487 * addresses for color and z have inner and outer step values,
488 * so that we can increment them appropriately. This method
489 * eliminates the need to adjust parameters by creeping a
490 * sub-pixel amount into the triangle at each scanline.
495 GLfixed fxLeftEdge
= 0, fxRightEdge
= 0;
496 GLfixed fdxLeftEdge
= 0, fdxRightEdge
= 0;
497 GLfixed fError
= 0, fdError
= 0;
499 PIXEL_TYPE
*pRow
= NULL
;
500 GLint dPRowOuter
= 0, dPRowInner
; /* offset in bytes */
504 struct gl_renderbuffer
*zrb
505 = ctx
->DrawBuffer
->Attachment
[BUFFER_DEPTH
].Renderbuffer
;
506 DEPTH_TYPE
*zRow
= NULL
;
507 GLint dZRowOuter
= 0, dZRowInner
; /* offset in bytes */
510 GLfixed fdzOuter
= 0, fdzInner
;
513 GLint rLeft
= 0, fdrOuter
= 0, fdrInner
;
514 GLint gLeft
= 0, fdgOuter
= 0, fdgInner
;
515 GLint bLeft
= 0, fdbOuter
= 0, fdbInner
;
518 GLint aLeft
= 0, fdaOuter
= 0, fdaInner
;
520 #ifdef INTERP_INT_TEX
521 GLfixed sLeft
=0, dsOuter
=0, dsInner
;
522 GLfixed tLeft
=0, dtOuter
=0, dtInner
;
524 #ifdef INTERP_ATTRIBS
525 GLfloat wLeft
= 0, dwOuter
= 0, dwInner
;
526 GLfloat attrLeft
[VARYING_SLOT_MAX
][4];
527 GLfloat daOuter
[VARYING_SLOT_MAX
][4], daInner
[VARYING_SLOT_MAX
][4];
530 for (subTriangle
=0; subTriangle
<=1; subTriangle
++) {
531 EdgeT
*eLeft
, *eRight
;
532 int setupLeft
, setupRight
;
535 if (subTriangle
==0) {
537 if (scan_from_left_to_right
) {
540 lines
= eRight
->lines
;
547 lines
= eLeft
->lines
;
554 if (scan_from_left_to_right
) {
557 lines
= eRight
->lines
;
564 lines
= eLeft
->lines
;
572 if (setupLeft
&& eLeft
->lines
> 0) {
573 const SWvertex
*vLower
= eLeft
->v0
;
574 const GLfixed fsy
= eLeft
->fsy
;
575 const GLfixed fsx
= eLeft
->fsx
; /* no fractional part */
576 const GLfixed fx
= FixedCeil(fsx
); /* no fractional part */
577 const GLfixed adjx
= (GLfixed
) (fx
- eLeft
->fx0
); /* SCALED! */
578 const GLfixed adjy
= (GLfixed
) eLeft
->adjy
; /* SCALED! */
583 fError
= fx
- fsx
- FIXED_ONE
;
584 fxLeftEdge
= fsx
- FIXED_EPSILON
;
585 fdxLeftEdge
= eLeft
->fdxdy
;
586 fdxOuter
= FixedFloor(fdxLeftEdge
- FIXED_EPSILON
);
587 fdError
= fdxOuter
- fdxLeftEdge
+ FIXED_ONE
;
588 idxOuter
= FixedToInt(fdxOuter
);
589 dxOuter
= (GLfloat
) idxOuter
;
590 span
.y
= FixedToInt(fsy
);
592 /* silence warnings on some compilers */
600 pRow
= (PIXEL_TYPE
*) PIXEL_ADDRESS(FixedToInt(fxLeftEdge
), span
.y
);
601 dPRowOuter
= -((int)BYTES_PER_ROW
) + idxOuter
* sizeof(PIXEL_TYPE
);
602 /* negative because Y=0 at bottom and increases upward */
606 * Now we need the set of parameter (z, color, etc.) values at
607 * the point (fx, fsy). This gives us properly-sampled parameter
608 * values that we can step from pixel to pixel. Furthermore,
609 * although we might have intermediate results that overflow
610 * the normal parameter range when we step temporarily outside
611 * the triangle, we shouldn't overflow or underflow for any
612 * pixel that's actually inside the triangle.
617 GLfloat z0
= vLower
->attrib
[VARYING_SLOT_POS
][2];
618 if (depthBits
<= 16) {
619 /* interpolate fixed-pt values */
620 GLfloat tmp
= (z0
* FIXED_SCALE
621 + span
.attrStepX
[VARYING_SLOT_POS
][2] * adjx
622 + span
.attrStepY
[VARYING_SLOT_POS
][2] * adjy
) + FIXED_HALF
;
623 if (tmp
< MAX_GLUINT
/ 2)
624 zLeft
= (GLfixed
) tmp
;
626 zLeft
= MAX_GLUINT
/ 2;
627 fdzOuter
= SignedFloatToFixed(span
.attrStepY
[VARYING_SLOT_POS
][2] +
628 dxOuter
* span
.attrStepX
[VARYING_SLOT_POS
][2]);
631 /* interpolate depth values w/out scaling */
632 zLeft
= (GLuint
) (z0
+ span
.attrStepX
[VARYING_SLOT_POS
][2] * FixedToFloat(adjx
)
633 + span
.attrStepY
[VARYING_SLOT_POS
][2] * FixedToFloat(adjy
));
634 fdzOuter
= (GLint
) (span
.attrStepY
[VARYING_SLOT_POS
][2] +
635 dxOuter
* span
.attrStepX
[VARYING_SLOT_POS
][2]);
638 zRow
= (DEPTH_TYPE
*)
639 _swrast_pixel_address(zrb
, FixedToInt(fxLeftEdge
), span
.y
);
640 dZRowOuter
= (ctx
->DrawBuffer
->Width
+ idxOuter
) * sizeof(DEPTH_TYPE
);
645 if (ctx
->Light
.ShadeModel
== GL_SMOOTH
) {
646 rLeft
= (GLint
)(ChanToFixed(vLower
->color
[RCOMP
])
647 + span
.attrStepX
[VARYING_SLOT_COL0
][0] * adjx
648 + span
.attrStepY
[VARYING_SLOT_COL0
][0] * adjy
) + FIXED_HALF
;
649 gLeft
= (GLint
)(ChanToFixed(vLower
->color
[GCOMP
])
650 + span
.attrStepX
[VARYING_SLOT_COL0
][1] * adjx
651 + span
.attrStepY
[VARYING_SLOT_COL0
][1] * adjy
) + FIXED_HALF
;
652 bLeft
= (GLint
)(ChanToFixed(vLower
->color
[BCOMP
])
653 + span
.attrStepX
[VARYING_SLOT_COL0
][2] * adjx
654 + span
.attrStepY
[VARYING_SLOT_COL0
][2] * adjy
) + FIXED_HALF
;
655 fdrOuter
= SignedFloatToFixed(span
.attrStepY
[VARYING_SLOT_COL0
][0]
656 + dxOuter
* span
.attrStepX
[VARYING_SLOT_COL0
][0]);
657 fdgOuter
= SignedFloatToFixed(span
.attrStepY
[VARYING_SLOT_COL0
][1]
658 + dxOuter
* span
.attrStepX
[VARYING_SLOT_COL0
][1]);
659 fdbOuter
= SignedFloatToFixed(span
.attrStepY
[VARYING_SLOT_COL0
][2]
660 + dxOuter
* span
.attrStepX
[VARYING_SLOT_COL0
][2]);
662 aLeft
= (GLint
)(ChanToFixed(vLower
->color
[ACOMP
])
663 + span
.attrStepX
[VARYING_SLOT_COL0
][3] * adjx
664 + span
.attrStepY
[VARYING_SLOT_COL0
][3] * adjy
) + FIXED_HALF
;
665 fdaOuter
= SignedFloatToFixed(span
.attrStepY
[VARYING_SLOT_COL0
][3]
666 + dxOuter
* span
.attrStepX
[VARYING_SLOT_COL0
][3]);
670 assert(ctx
->Light
.ShadeModel
== GL_FLAT
);
671 rLeft
= ChanToFixed(v2
->color
[RCOMP
]);
672 gLeft
= ChanToFixed(v2
->color
[GCOMP
]);
673 bLeft
= ChanToFixed(v2
->color
[BCOMP
]);
674 fdrOuter
= fdgOuter
= fdbOuter
= 0;
676 aLeft
= ChanToFixed(v2
->color
[ACOMP
]);
680 #endif /* INTERP_RGB */
683 #ifdef INTERP_INT_TEX
686 s0
= vLower
->attrib
[VARYING_SLOT_TEX0
][0] * S_SCALE
;
687 sLeft
= (GLfixed
)(s0
* FIXED_SCALE
+ span
.attrStepX
[VARYING_SLOT_TEX0
][0] * adjx
688 + span
.attrStepY
[VARYING_SLOT_TEX0
][0] * adjy
) + FIXED_HALF
;
689 dsOuter
= SignedFloatToFixed(span
.attrStepY
[VARYING_SLOT_TEX0
][0]
690 + dxOuter
* span
.attrStepX
[VARYING_SLOT_TEX0
][0]);
692 t0
= vLower
->attrib
[VARYING_SLOT_TEX0
][1] * T_SCALE
;
693 tLeft
= (GLfixed
)(t0
* FIXED_SCALE
+ span
.attrStepX
[VARYING_SLOT_TEX0
][1] * adjx
694 + span
.attrStepY
[VARYING_SLOT_TEX0
][1] * adjy
) + FIXED_HALF
;
695 dtOuter
= SignedFloatToFixed(span
.attrStepY
[VARYING_SLOT_TEX0
][1]
696 + dxOuter
* span
.attrStepX
[VARYING_SLOT_TEX0
][1]);
699 #ifdef INTERP_ATTRIBS
701 const GLuint attr
= VARYING_SLOT_POS
;
702 wLeft
= vLower
->attrib
[VARYING_SLOT_POS
][3]
703 + (span
.attrStepX
[attr
][3] * adjx
704 + span
.attrStepY
[attr
][3] * adjy
) * (1.0F
/FIXED_SCALE
);
705 dwOuter
= span
.attrStepY
[attr
][3] + dxOuter
* span
.attrStepX
[attr
][3];
708 const GLfloat invW
= vLower
->attrib
[VARYING_SLOT_POS
][3];
709 if (swrast
->_InterpMode
[attr
] == GL_FLAT
) {
711 for (c
= 0; c
< 4; c
++) {
712 attrLeft
[attr
][c
] = v2
->attrib
[attr
][c
] * invW
;
713 daOuter
[attr
][c
] = 0.0;
718 for (c
= 0; c
< 4; c
++) {
719 const GLfloat a
= vLower
->attrib
[attr
][c
] * invW
;
720 attrLeft
[attr
][c
] = a
+ ( span
.attrStepX
[attr
][c
] * adjx
721 + span
.attrStepY
[attr
][c
] * adjy
) * (1.0F
/FIXED_SCALE
);
722 daOuter
[attr
][c
] = span
.attrStepY
[attr
][c
] + dxOuter
* span
.attrStepX
[attr
][c
];
730 if (setupRight
&& eRight
->lines
>0) {
731 fxRightEdge
= eRight
->fsx
- FIXED_EPSILON
;
732 fdxRightEdge
= eRight
->fdxdy
;
740 /* Rasterize setup */
742 dPRowInner
= dPRowOuter
+ sizeof(PIXEL_TYPE
);
746 dZRowInner
= dZRowOuter
+ sizeof(DEPTH_TYPE
);
748 fdzInner
= fdzOuter
+ span
.zStep
;
751 fdrInner
= fdrOuter
+ span
.redStep
;
752 fdgInner
= fdgOuter
+ span
.greenStep
;
753 fdbInner
= fdbOuter
+ span
.blueStep
;
756 fdaInner
= fdaOuter
+ span
.alphaStep
;
758 #ifdef INTERP_INT_TEX
759 dsInner
= dsOuter
+ span
.intTexStep
[0];
760 dtInner
= dtOuter
+ span
.intTexStep
[1];
762 #ifdef INTERP_ATTRIBS
763 dwInner
= dwOuter
+ span
.attrStepX
[VARYING_SLOT_POS
][3];
766 for (c
= 0; c
< 4; c
++) {
767 daInner
[attr
][c
] = daOuter
[attr
][c
] + span
.attrStepX
[attr
][c
];
773 /* initialize the span interpolants to the leftmost value */
774 /* ff = fixed-pt fragment */
775 const GLint right
= FixedToInt(fxRightEdge
);
776 span
.x
= FixedToInt(fxLeftEdge
);
780 span
.end
= right
- span
.x
;
793 #ifdef INTERP_INT_TEX
794 span
.intTex
[0] = sLeft
;
795 span
.intTex
[1] = tLeft
;
798 #ifdef INTERP_ATTRIBS
799 span
.attrStart
[VARYING_SLOT_POS
][3] = wLeft
;
802 for (c
= 0; c
< 4; c
++) {
803 span
.attrStart
[attr
][c
] = attrLeft
[attr
][c
];
808 /* This is where we actually generate fragments */
809 /* XXX the test for span.y > 0 _shouldn't_ be needed but
810 * it fixes a problem on 64-bit Opterons (bug 4842).
812 if (span
.end
> 0 && span
.y
>= 0) {
813 const GLint len
= span
.end
- 1;
816 CLAMP_INTERPOLANT(red
, redStep
, len
);
817 CLAMP_INTERPOLANT(green
, greenStep
, len
);
818 CLAMP_INTERPOLANT(blue
, blueStep
, len
);
821 CLAMP_INTERPOLANT(alpha
, alphaStep
, len
);
829 * Advance to the next scan line. Compute the
830 * new edge coordinates, and adjust the
831 * pixel-center x coordinate so that it stays
832 * on or inside the major edge.
837 fxLeftEdge
+= fdxLeftEdge
;
838 fxRightEdge
+= fdxRightEdge
;
845 pRow
= (PIXEL_TYPE
*) ((GLubyte
*) pRow
+ dPRowOuter
);
849 zRow
= (DEPTH_TYPE
*) ((GLubyte
*) zRow
+ dZRowOuter
);
861 #ifdef INTERP_INT_TEX
865 #ifdef INTERP_ATTRIBS
869 for (c
= 0; c
< 4; c
++) {
870 attrLeft
[attr
][c
] += daOuter
[attr
][c
];
877 pRow
= (PIXEL_TYPE
*) ((GLubyte
*) pRow
+ dPRowInner
);
881 zRow
= (DEPTH_TYPE
*) ((GLubyte
*) zRow
+ dZRowInner
);
893 #ifdef INTERP_INT_TEX
897 #ifdef INTERP_ATTRIBS
901 for (c
= 0; c
< 4; c
++) {
902 attrLeft
[attr
][c
] += daInner
[attr
][c
];
909 } /* for subTriangle */
926 #undef INTERP_INT_TEX
927 #undef INTERP_ATTRIBS