src/mesa/swrast/s_aatriangle.c

   1 /*
   2  * Mesa 3-D graphics library
   3  * Version:  6.5.3
   4  *
   5  * Copyright (C) 1999-2007  Brian Paul   All Rights Reserved.
   6  *
   7  * Permission is hereby granted, free of charge, to any person obtaining a
   8  * copy of this software and associated documentation files (the "Software"),
   9  * to deal in the Software without restriction, including without limitation
  10  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
  11  * and/or sell copies of the Software, and to permit persons to whom the
  12  * Software is furnished to do so, subject to the following conditions:
  13  *
  14  * The above copyright notice and this permission notice shall be included
  15  * in all copies or substantial portions of the Software.
  16  *
  17  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  18  * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  19  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  20  * BRIAN PAUL BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
  21  * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  22  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  23  */
  24
  25
  26 /*
  27  * Antialiased Triangle rasterizers
  28  */
  29
  30
  31 #include "main/glheader.h"
  32 #include "main/context.h"
  33 #include "main/colormac.h"
  34 #include "main/macros.h"
  35 #include "main/imports.h"
  36 #include "s_aatriangle.h"
  37 #include "s_context.h"
  38 #include "s_span.h"
  39
  40
  41 /*
  42  * Compute coefficients of a plane using the X,Y coords of the v0, v1, v2
  43  * vertices and the given Z values.
  44  * A point (x,y,z) lies on plane iff a*x+b*y+c*z+d = 0.
  45  */
  46 static INLINE void
  47 compute_plane(const GLfloat v0[], const GLfloat v1[], const GLfloat v2[],
  48               GLfloat z0, GLfloat z1, GLfloat z2, GLfloat plane[4])
  49 {
  50    const GLfloat px = v1[0] - v0[0];
  51    const GLfloat py = v1[1] - v0[1];
  52    const GLfloat pz = z1 - z0;
  53
  54    const GLfloat qx = v2[0] - v0[0];
  55    const GLfloat qy = v2[1] - v0[1];
  56    const GLfloat qz = z2 - z0;
  57
  58    /* Crossproduct "(a,b,c):= dv1 x dv2" is orthogonal to plane. */
  59    const GLfloat a = py * qz - pz * qy;
  60    const GLfloat b = pz * qx - px * qz;
  61    const GLfloat c = px * qy - py * qx;
  62    /* Point on the plane = "r*(a,b,c) + w", with fixed "r" depending
  63       on the distance of plane from origin and arbitrary "w" parallel
  64       to the plane. */
  65    /* The scalar product "(r*(a,b,c)+w)*(a,b,c)" is "r*(a^2+b^2+c^2)",
  66       which is equal to "-d" below. */
  67    const GLfloat d = -(a * v0[0] + b * v0[1] + c * z0);
  68
  69    plane[0] = a;
  70    plane[1] = b;
  71    plane[2] = c;
  72    plane[3] = d;
  73 }
  74
  75
  76 /*
  77  * Compute coefficients of a plane with a constant Z value.
  78  */
  79 static INLINE void
  80 constant_plane(GLfloat value, GLfloat plane[4])
  81 {
  82    plane[0] = 0.0;
  83    plane[1] = 0.0;
  84    plane[2] = -1.0;
  85    plane[3] = value;
  86 }
  87
  88 #define CONSTANT_PLANE(VALUE, PLANE)    \
  89 do {                                    \
  90    PLANE[0] = 0.0F;                     \
  91    PLANE[1] = 0.0F;                     \
  92    PLANE[2] = -1.0F;                    \
  93    PLANE[3] = VALUE;                    \
  94 } while (0)
  95
  96
  97
  98 /*
  99  * Solve plane equation for Z at (X,Y).
 100  */
 101 static INLINE GLfloat
 102 solve_plane(GLfloat x, GLfloat y, const GLfloat plane[4])
 103 {
 104    ASSERT(plane[2] != 0.0F);
 105    return (plane[3] + plane[0] * x + plane[1] * y) / -plane[2];
 106 }
 107
 108
 109 #define SOLVE_PLANE(X, Y, PLANE) \
 110    ((PLANE[3] + PLANE[0] * (X) + PLANE[1] * (Y)) / -PLANE[2])
 111
 112
 113 /*
 114  * Return 1 / solve_plane().
 115  */
 116 static INLINE GLfloat
 117 solve_plane_recip(GLfloat x, GLfloat y, const GLfloat plane[4])
 118 {
 119    const GLfloat denom = plane[3] + plane[0] * x + plane[1] * y;
 120    if (denom == 0.0F)
 121       return 0.0F;
 122    else
 123       return -plane[2] / denom;
 124 }
 125
 126
 127 /*
 128  * Solve plane and return clamped GLchan value.
 129  */
 130 static INLINE GLchan
 131 solve_plane_chan(GLfloat x, GLfloat y, const GLfloat plane[4])
 132 {
 133    const GLfloat z = (plane[3] + plane[0] * x + plane[1] * y) / -plane[2];
 134 #if CHAN_TYPE == GL_FLOAT
 135    return CLAMP(z, 0.0F, CHAN_MAXF);
 136 #else
 137    if (z < 0)
 138       return 0;
 139    else if (z > CHAN_MAX)
 140       return CHAN_MAX;
 141    return (GLchan) IROUND_POS(z);
 142 #endif
 143 }
 144
 145
 146 static INLINE GLfloat
 147 plane_dx(const GLfloat plane[4])
 148 {
 149    return -plane[0] / plane[2];
 150 }
 151
 152 static INLINE GLfloat
 153 plane_dy(const GLfloat plane[4])
 154 {
 155    return -plane[1] / plane[2];
 156 }
 157
 158
 159
 160 /*
 161  * Compute how much (area) of the given pixel is inside the triangle.
 162  * Vertices MUST be specified in counter-clockwise order.
 163  * Return:  coverage in [0, 1].
 164  */
 165 static GLfloat
 166 compute_coveragef(const GLfloat v0[3], const GLfloat v1[3],
 167                   const GLfloat v2[3], GLint winx, GLint winy)
 168 {
 169    /* Given a position [0,3]x[0,3] return the sub-pixel sample position.
 170     * Contributed by Ray Tice.
 171     *
 172     * Jitter sample positions -
 173     * - average should be .5 in x & y for each column
 174     * - each of the 16 rows and columns should be used once
 175     * - the rectangle formed by the first four points
 176     *   should contain the other points
 177     * - the distrubition should be fairly even in any given direction
 178     *
 179     * The pattern drawn below isn't optimal, but it's better than a regular
 180     * grid.  In the drawing, the center of each subpixel is surrounded by
 181     * four dots.  The "x" marks the jittered position relative to the
 182     * subpixel center.
 183     */
 184 #define POS(a, b) (0.5+a*4+b)/16
 185    static const GLfloat samples[16][2] = {
 186       /* start with the four corners */
 187       { POS(0, 2), POS(0, 0) },
 188       { POS(3, 3), POS(0, 2) },
 189       { POS(0, 0), POS(3, 1) },
 190       { POS(3, 1), POS(3, 3) },
 191       /* continue with interior samples */
 192       { POS(1, 1), POS(0, 1) },
 193       { POS(2, 0), POS(0, 3) },
 194       { POS(0, 3), POS(1, 3) },
 195       { POS(1, 2), POS(1, 0) },
 196       { POS(2, 3), POS(1, 2) },
 197       { POS(3, 2), POS(1, 1) },
 198       { POS(0, 1), POS(2, 2) },
 199       { POS(1, 0), POS(2, 1) },
 200       { POS(2, 1), POS(2, 3) },
 201       { POS(3, 0), POS(2, 0) },
 202       { POS(1, 3), POS(3, 0) },
 203       { POS(2, 2), POS(3, 2) }
 204    };
 205
 206    const GLfloat x = (GLfloat) winx;
 207    const GLfloat y = (GLfloat) winy;
 208    const GLfloat dx0 = v1[0] - v0[0];
 209    const GLfloat dy0 = v1[1] - v0[1];
 210    const GLfloat dx1 = v2[0] - v1[0];
 211    const GLfloat dy1 = v2[1] - v1[1];
 212    const GLfloat dx2 = v0[0] - v2[0];
 213    const GLfloat dy2 = v0[1] - v2[1];
 214    GLint stop = 4, i;
 215    GLfloat insideCount = 16.0F;
 216
 217 #ifdef DEBUG
 218    {
 219       const GLfloat area = dx0 * dy1 - dx1 * dy0;
 220       ASSERT(area >= 0.0);
 221    }
 222 #endif
 223
 224    for (i = 0; i < stop; i++) {
 225       const GLfloat sx = x + samples[i][0];
 226       const GLfloat sy = y + samples[i][1];
 227       /* cross product determines if sample is inside or outside each edge */
 228       GLfloat cross = (dx0 * (sy - v0[1]) - dy0 * (sx - v0[0]));
 229       /* Check if the sample is exactly on an edge.  If so, let cross be a
 230        * positive or negative value depending on the direction of the edge.
 231        */
 232       if (cross == 0.0F)
 233          cross = dx0 + dy0;
 234       if (cross < 0.0F) {
 235          /* sample point is outside first edge */
 236          insideCount -= 1.0F;
 237          stop = 16;
 238       }
 239       else {
 240          /* sample point is inside first edge */
 241          cross = (dx1 * (sy - v1[1]) - dy1 * (sx - v1[0]));
 242          if (cross == 0.0F)
 243             cross = dx1 + dy1;
 244          if (cross < 0.0F) {
 245             /* sample point is outside second edge */
 246             insideCount -= 1.0F;
 247             stop = 16;
 248          }
 249          else {
 250             /* sample point is inside first and second edges */
 251             cross = (dx2 * (sy - v2[1]) -  dy2 * (sx - v2[0]));
 252             if (cross == 0.0F)
 253                cross = dx2 + dy2;
 254             if (cross < 0.0F) {
 255                /* sample point is outside third edge */
 256                insideCount -= 1.0F;
 257                stop = 16;
 258             }
 259          }
 260       }
 261    }
 262    if (stop == 4)
 263       return 1.0F;
 264    else
 265       return insideCount * (1.0F / 16.0F);
 266 }
 267
 268
 269
 270 static void
 271 rgba_aa_tri(GLcontext *ctx,
 272             const SWvertex *v0,
 273             const SWvertex *v1,
 274             const SWvertex *v2)
 275 {
 276 #define DO_Z
 277 #include "s_aatritemp.h"
 278 }
 279
 280
 281 static void
 282 general_aa_tri(GLcontext *ctx,
 283                const SWvertex *v0,
 284                const SWvertex *v1,
 285                const SWvertex *v2)
 286 {
 287 #define DO_Z
 288 #define DO_ATTRIBS
 289 #include "s_aatritemp.h"
 290 }
 291
 292
 293
 294 /*
 295  * Examine GL state and set swrast->Triangle to an
 296  * appropriate antialiased triangle rasterizer function.
 297  */
 298 void
 299 _swrast_set_aa_triangle_function(GLcontext *ctx)
 300 {
 301    SWcontext *swrast = SWRAST_CONTEXT(ctx);
 302
 303    ASSERT(ctx->Polygon.SmoothFlag);
 304
 305    if (ctx->Texture._EnabledCoordUnits != 0
 306        || ctx->FragmentProgram._Current
 307        || swrast->_FogEnabled
 308        || NEED_SECONDARY_COLOR(ctx)) {
 309       SWRAST_CONTEXT(ctx)->Triangle = general_aa_tri;
 310    }
 311    else {
 312       SWRAST_CONTEXT(ctx)->Triangle = rgba_aa_tri;
 313    }
 314
 315    ASSERT(SWRAST_CONTEXT(ctx)->Triangle);
 316 }