src/mesa/swrast/s_aatriangle.c

   1 /*
   2  * Mesa 3-D graphics library
   3  *
   4  * Copyright (C) 1999-2007  Brian Paul   All Rights Reserved.
   5  *
   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:
  12  *
  13  * The above copyright notice and this permission notice shall be included
  14  * in all copies or substantial portions of the Software.
  15  *
  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.
  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 "main/state.h"
  37 #include "s_aatriangle.h"
  38 #include "s_context.h"
  39 #include "s_span.h"
  40
  41
  42 /*
  43  * Compute coefficients of a plane using the X,Y coords of the v0, v1, v2
  44  * vertices and the given Z values.
  45  * A point (x,y,z) lies on plane iff a*x+b*y+c*z+d = 0.
  46  */
  47 static inline void
  48 compute_plane(const GLfloat v0[], const GLfloat v1[], const GLfloat v2[],
  49               GLfloat z0, GLfloat z1, GLfloat z2, GLfloat plane[4])
  50 {
  51    const GLfloat px = v1[0] - v0[0];
  52    const GLfloat py = v1[1] - v0[1];
  53    const GLfloat pz = z1 - z0;
  54
  55    const GLfloat qx = v2[0] - v0[0];
  56    const GLfloat qy = v2[1] - v0[1];
  57    const GLfloat qz = z2 - z0;
  58
  59    /* Crossproduct "(a,b,c):= dv1 x dv2" is orthogonal to plane. */
  60    const GLfloat a = py * qz - pz * qy;
  61    const GLfloat b = pz * qx - px * qz;
  62    const GLfloat c = px * qy - py * qx;
  63    /* Point on the plane = "r*(a,b,c) + w", with fixed "r" depending
  64       on the distance of plane from origin and arbitrary "w" parallel
  65       to the plane. */
  66    /* The scalar product "(r*(a,b,c)+w)*(a,b,c)" is "r*(a^2+b^2+c^2)",
  67       which is equal to "-d" below. */
  68    const GLfloat d = -(a * v0[0] + b * v0[1] + c * z0);
  69
  70    plane[0] = a;
  71    plane[1] = b;
  72    plane[2] = c;
  73    plane[3] = d;
  74 }
  75
  76
  77 /*
  78  * Compute coefficients of a plane with a constant Z value.
  79  */
  80 static inline void
  81 constant_plane(GLfloat value, GLfloat plane[4])
  82 {
  83    plane[0] = 0.0;
  84    plane[1] = 0.0;
  85    plane[2] = -1.0;
  86    plane[3] = value;
  87 }
  88
  89 #define CONSTANT_PLANE(VALUE, PLANE)    \
  90 do {                                    \
  91    PLANE[0] = 0.0F;                     \
  92    PLANE[1] = 0.0F;                     \
  93    PLANE[2] = -1.0F;                    \
  94    PLANE[3] = VALUE;                    \
  95 } while (0)
  96
  97
  98
  99 /*
 100  * Solve plane equation for Z at (X,Y).
 101  */
 102 static inline GLfloat
 103 solve_plane(GLfloat x, GLfloat y, const GLfloat plane[4])
 104 {
 105    ASSERT(plane[2] != 0.0F);
 106    return (plane[3] + plane[0] * x + plane[1] * y) / -plane[2];
 107 }
 108
 109
 110 #define SOLVE_PLANE(X, Y, PLANE) \
 111    ((PLANE[3] + PLANE[0] * (X) + PLANE[1] * (Y)) / -PLANE[2])
 112
 113
 114 /*
 115  * Solve plane and return clamped GLchan value.
 116  */
 117 static inline GLchan
 118 solve_plane_chan(GLfloat x, GLfloat y, const GLfloat plane[4])
 119 {
 120    const GLfloat z = (plane[3] + plane[0] * x + plane[1] * y) / -plane[2];
 121 #if CHAN_TYPE == GL_FLOAT
 122    return CLAMP(z, 0.0F, CHAN_MAXF);
 123 #else
 124    if (z < 0)
 125       return 0;
 126    else if (z > CHAN_MAX)
 127       return CHAN_MAX;
 128    return (GLchan) IROUND_POS(z);
 129 #endif
 130 }
 131
 132
 133 static inline GLfloat
 134 plane_dx(const GLfloat plane[4])
 135 {
 136    return -plane[0] / plane[2];
 137 }
 138
 139 static inline GLfloat
 140 plane_dy(const GLfloat plane[4])
 141 {
 142    return -plane[1] / plane[2];
 143 }
 144
 145
 146
 147 /*
 148  * Compute how much (area) of the given pixel is inside the triangle.
 149  * Vertices MUST be specified in counter-clockwise order.
 150  * Return:  coverage in [0, 1].
 151  */
 152 static GLfloat
 153 compute_coveragef(const GLfloat v0[3], const GLfloat v1[3],
 154                   const GLfloat v2[3], GLint winx, GLint winy)
 155 {
 156    /* Given a position [0,3]x[0,3] return the sub-pixel sample position.
 157     * Contributed by Ray Tice.
 158     *
 159     * Jitter sample positions -
 160     * - average should be .5 in x & y for each column
 161     * - each of the 16 rows and columns should be used once
 162     * - the rectangle formed by the first four points
 163     *   should contain the other points
 164     * - the distrubition should be fairly even in any given direction
 165     *
 166     * The pattern drawn below isn't optimal, but it's better than a regular
 167     * grid.  In the drawing, the center of each subpixel is surrounded by
 168     * four dots.  The "x" marks the jittered position relative to the
 169     * subpixel center.
 170     */
 171 #define POS(a, b) (0.5+a*4+b)/16
 172    static const GLfloat samples[16][2] = {
 173       /* start with the four corners */
 174       { POS(0, 2), POS(0, 0) },
 175       { POS(3, 3), POS(0, 2) },
 176       { POS(0, 0), POS(3, 1) },
 177       { POS(3, 1), POS(3, 3) },
 178       /* continue with interior samples */
 179       { POS(1, 1), POS(0, 1) },
 180       { POS(2, 0), POS(0, 3) },
 181       { POS(0, 3), POS(1, 3) },
 182       { POS(1, 2), POS(1, 0) },
 183       { POS(2, 3), POS(1, 2) },
 184       { POS(3, 2), POS(1, 1) },
 185       { POS(0, 1), POS(2, 2) },
 186       { POS(1, 0), POS(2, 1) },
 187       { POS(2, 1), POS(2, 3) },
 188       { POS(3, 0), POS(2, 0) },
 189       { POS(1, 3), POS(3, 0) },
 190       { POS(2, 2), POS(3, 2) }
 191    };
 192
 193    const GLfloat x = (GLfloat) winx;
 194    const GLfloat y = (GLfloat) winy;
 195    const GLfloat dx0 = v1[0] - v0[0];
 196    const GLfloat dy0 = v1[1] - v0[1];
 197    const GLfloat dx1 = v2[0] - v1[0];
 198    const GLfloat dy1 = v2[1] - v1[1];
 199    const GLfloat dx2 = v0[0] - v2[0];
 200    const GLfloat dy2 = v0[1] - v2[1];
 201    GLint stop = 4, i;
 202    GLfloat insideCount = 16.0F;
 203
 204    ASSERT(dx0 * dy1 - dx1 * dy0 >= 0.0); /* area >= 0.0 */
 205
 206    for (i = 0; i < stop; i++) {
 207       const GLfloat sx = x + samples[i][0];
 208       const GLfloat sy = y + samples[i][1];
 209       /* cross product determines if sample is inside or outside each edge */
 210       GLfloat cross = (dx0 * (sy - v0[1]) - dy0 * (sx - v0[0]));
 211       /* Check if the sample is exactly on an edge.  If so, let cross be a
 212        * positive or negative value depending on the direction of the edge.
 213        */
 214       if (cross == 0.0F)
 215          cross = dx0 + dy0;
 216       if (cross < 0.0F) {
 217          /* sample point is outside first edge */
 218          insideCount -= 1.0F;
 219          stop = 16;
 220       }
 221       else {
 222          /* sample point is inside first edge */
 223          cross = (dx1 * (sy - v1[1]) - dy1 * (sx - v1[0]));
 224          if (cross == 0.0F)
 225             cross = dx1 + dy1;
 226          if (cross < 0.0F) {
 227             /* sample point is outside second edge */
 228             insideCount -= 1.0F;
 229             stop = 16;
 230          }
 231          else {
 232             /* sample point is inside first and second edges */
 233             cross = (dx2 * (sy - v2[1]) -  dy2 * (sx - v2[0]));
 234             if (cross == 0.0F)
 235                cross = dx2 + dy2;
 236             if (cross < 0.0F) {
 237                /* sample point is outside third edge */
 238                insideCount -= 1.0F;
 239                stop = 16;
 240             }
 241          }
 242       }
 243    }
 244    if (stop == 4)
 245       return 1.0F;
 246    else
 247       return insideCount * (1.0F / 16.0F);
 248 }
 249
 250
 251
 252 static void
 253 rgba_aa_tri(struct gl_context *ctx,
 254             const SWvertex *v0,
 255             const SWvertex *v1,
 256             const SWvertex *v2)
 257 {
 258 #define DO_Z
 259 #include "s_aatritemp.h"
 260 }
 261
 262
 263 static void
 264 general_aa_tri(struct gl_context *ctx,
 265                const SWvertex *v0,
 266                const SWvertex *v1,
 267                const SWvertex *v2)
 268 {
 269 #define DO_Z
 270 #define DO_ATTRIBS
 271 #include "s_aatritemp.h"
 272 }
 273
 274
 275
 276 /*
 277  * Examine GL state and set swrast->Triangle to an
 278  * appropriate antialiased triangle rasterizer function.
 279  */
 280 void
 281 _swrast_set_aa_triangle_function(struct gl_context *ctx)
 282 {
 283    SWcontext *swrast = SWRAST_CONTEXT(ctx);
 284
 285    ASSERT(ctx->Polygon.SmoothFlag);
 286
 287    if (ctx->Texture._EnabledCoordUnits != 0
 288        || _swrast_use_fragment_program(ctx)
 289        || swrast->_FogEnabled
 290        || _mesa_need_secondary_color(ctx)) {
 291       SWRAST_CONTEXT(ctx)->Triangle = general_aa_tri;
 292    }
 293    else {
 294       SWRAST_CONTEXT(ctx)->Triangle = rgba_aa_tri;
 295    }
 296
 297    ASSERT(SWRAST_CONTEXT(ctx)->Triangle);
 298 }