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