xref: /xsrc/external/mit/MesaLib/dist/src/mesa/swrast/s_aatriangle.c

/*
 * Mesa 3-D graphics library
 *
 * Copyright (C) 1999-2007  Brian Paul   All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 */


/*
 * Antialiased Triangle rasterizers
 */


#include "main/glheader.h"
#include "main/context.h"
#include "main/macros.h"
#include "main/state.h"
#include "s_aatriangle.h"
#include "s_context.h"
#include "s_span.h"


/*
 * Compute coefficients of a plane using the X,Y coords of the v0, v1, v2
 * vertices and the given Z values.
 * A point (x,y,z) lies on plane iff a*x+b*y+c*z+d = 0.
 */
static inline void
compute_plane(const GLfloat v0[], const GLfloat v1[], const GLfloat v2[],
              GLfloat z0, GLfloat z1, GLfloat z2, GLfloat plane[4])
{
   const GLfloat px = v1[0] - v0[0];
   const GLfloat py = v1[1] - v0[1];
   const GLfloat pz = z1 - z0;

   const GLfloat qx = v2[0] - v0[0];
   const GLfloat qy = v2[1] - v0[1];
   const GLfloat qz = z2 - z0;

   /* Crossproduct "(a,b,c):= dv1 x dv2" is orthogonal to plane. */
   const GLfloat a = py * qz - pz * qy;
   const GLfloat b = pz * qx - px * qz;
   const GLfloat c = px * qy - py * qx;
   /* Point on the plane = "r*(a,b,c) + w", with fixed "r" depending
      on the distance of plane from origin and arbitrary "w" parallel
      to the plane. */
   /* The scalar product "(r*(a,b,c)+w)*(a,b,c)" is "r*(a^2+b^2+c^2)",
      which is equal to "-d" below. */
   const GLfloat d = -(a * v0[0] + b * v0[1] + c * z0);

   plane[0] = a;
   plane[1] = b;
   plane[2] = c;
   plane[3] = d;
}


/*
 * Compute coefficients of a plane with a constant Z value.
 */
static inline void
constant_plane(GLfloat value, GLfloat plane[4])
{
   plane[0] = 0.0;
   plane[1] = 0.0;
   plane[2] = -1.0;
   plane[3] = value;
}

#define CONSTANT_PLANE(VALUE, PLANE)	\
do {					\
   PLANE[0] = 0.0F;			\
   PLANE[1] = 0.0F;			\
   PLANE[2] = -1.0F;			\
   PLANE[3] = VALUE;			\
} while (0)



/*
 * Solve plane equation for Z at (X,Y).
 */
static inline GLfloat
solve_plane(GLfloat x, GLfloat y, const GLfloat plane[4])
{
   assert(plane[2] != 0.0F);
   return (plane[3] + plane[0] * x + plane[1] * y) / -plane[2];
}


#define SOLVE_PLANE(X, Y, PLANE) \
   ((PLANE[3] + PLANE[0] * (X) + PLANE[1] * (Y)) / -PLANE[2])


/*
 * Solve plane and return clamped GLchan value.
 */
static inline GLchan
solve_plane_chan(GLfloat x, GLfloat y, const GLfloat plane[4])
{
   const GLfloat z = (plane[3] + plane[0] * x + plane[1] * y) / -plane[2];
#if CHAN_TYPE == GL_FLOAT
   return CLAMP(z, 0.0F, CHAN_MAXF);
#else
   if (z < 0)
      return 0;
   else if (z > CHAN_MAX)
      return CHAN_MAX;
   return (GLchan) lroundf(z);
#endif
}


static inline GLfloat
plane_dx(const GLfloat plane[4])
{
   return -plane[0] / plane[2];
}

static inline GLfloat
plane_dy(const GLfloat plane[4])
{
   return -plane[1] / plane[2];
}



/*
 * Compute how much (area) of the given pixel is inside the triangle.
 * Vertices MUST be specified in counter-clockwise order.
 * Return:  coverage in [0, 1].
 */
static GLfloat
compute_coveragef(const GLfloat v0[3], const GLfloat v1[3],
                  const GLfloat v2[3], GLint winx, GLint winy)
{
   /* Given a position [0,3]x[0,3] return the sub-pixel sample position.
    * Contributed by Ray Tice.
    *
    * Jitter sample positions -
    * - average should be .5 in x & y for each column
    * - each of the 16 rows and columns should be used once
    * - the rectangle formed by the first four points
    *   should contain the other points
    * - the distrubition should be fairly even in any given direction
    *
    * The pattern drawn below isn't optimal, but it's better than a regular
    * grid.  In the drawing, the center of each subpixel is surrounded by
    * four dots.  The "x" marks the jittered position relative to the
    * subpixel center.
    */
#define POS(a, b) (0.5+a*4+b)/16
   static const GLfloat samples[16][2] = {
      /* start with the four corners */
      { POS(0, 2), POS(0, 0) },
      { POS(3, 3), POS(0, 2) },
      { POS(0, 0), POS(3, 1) },
      { POS(3, 1), POS(3, 3) },
      /* continue with interior samples */
      { POS(1, 1), POS(0, 1) },
      { POS(2, 0), POS(0, 3) },
      { POS(0, 3), POS(1, 3) },
      { POS(1, 2), POS(1, 0) },
      { POS(2, 3), POS(1, 2) },
      { POS(3, 2), POS(1, 1) },
      { POS(0, 1), POS(2, 2) },
      { POS(1, 0), POS(2, 1) },
      { POS(2, 1), POS(2, 3) },
      { POS(3, 0), POS(2, 0) },
      { POS(1, 3), POS(3, 0) },
      { POS(2, 2), POS(3, 2) }
   };

   const GLfloat x = (GLfloat) winx;
   const GLfloat y = (GLfloat) winy;
   const GLfloat dx0 = v1[0] - v0[0];
   const GLfloat dy0 = v1[1] - v0[1];
   const GLfloat dx1 = v2[0] - v1[0];
   const GLfloat dy1 = v2[1] - v1[1];
   const GLfloat dx2 = v0[0] - v2[0];
   const GLfloat dy2 = v0[1] - v2[1];
   GLint stop = 4, i;
   GLfloat insideCount = 16.0F;

   assert(dx0 * dy1 - dx1 * dy0 >= 0.0); /* area >= 0.0 */

   for (i = 0; i < stop; i++) {
      const GLfloat sx = x + samples[i][0];
      const GLfloat sy = y + samples[i][1];
      /* cross product determines if sample is inside or outside each edge */
      GLfloat cross = (dx0 * (sy - v0[1]) - dy0 * (sx - v0[0]));
      /* Check if the sample is exactly on an edge.  If so, let cross be a
       * positive or negative value depending on the direction of the edge.
       */
      if (cross == 0.0F)
         cross = dx0 + dy0;
      if (cross < 0.0F) {
         /* sample point is outside first edge */
         insideCount -= 1.0F;
         stop = 16;
      }
      else {
         /* sample point is inside first edge */
         cross = (dx1 * (sy - v1[1]) - dy1 * (sx - v1[0]));
         if (cross == 0.0F)
            cross = dx1 + dy1;
         if (cross < 0.0F) {
            /* sample point is outside second edge */
            insideCount -= 1.0F;
            stop = 16;
         }
         else {
            /* sample point is inside first and second edges */
            cross = (dx2 * (sy - v2[1]) -  dy2 * (sx - v2[0]));
            if (cross == 0.0F)
               cross = dx2 + dy2;
            if (cross < 0.0F) {
               /* sample point is outside third edge */
               insideCount -= 1.0F;
               stop = 16;
            }
         }
      }
   }
   if (stop == 4)
      return 1.0F;
   else
      return insideCount * (1.0F / 16.0F);
}



static void
rgba_aa_tri(struct gl_context *ctx,
	    const SWvertex *v0,
	    const SWvertex *v1,
	    const SWvertex *v2)
{
#define DO_Z
#include "s_aatritemp.h"
}


static void
general_aa_tri(struct gl_context *ctx,
               const SWvertex *v0,
               const SWvertex *v1,
               const SWvertex *v2)
{
#define DO_Z
#define DO_ATTRIBS
#include "s_aatritemp.h"
}



/*
 * Examine GL state and set swrast->Triangle to an
 * appropriate antialiased triangle rasterizer function.
 */
void
_swrast_set_aa_triangle_function(struct gl_context *ctx)
{
   SWcontext *swrast = SWRAST_CONTEXT(ctx);

   assert(ctx->Polygon.SmoothFlag);

   if (ctx->Texture._EnabledCoordUnits != 0
       || _swrast_use_fragment_program(ctx)
       || swrast->_FogEnabled
       || _mesa_need_secondary_color(ctx)) {
      SWRAST_CONTEXT(ctx)->Triangle = general_aa_tri;
   }
   else {
      SWRAST_CONTEXT(ctx)->Triangle = rgba_aa_tri;
   }

   assert(SWRAST_CONTEXT(ctx)->Triangle);
}