src/mesa/pipe/draw/draw_offset.c

   1 /**************************************************************************
   2  *
   3  * Copyright 2007 Tungsten Graphics, Inc., Cedar Park, Texas.
   4  * 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
   8  * "Software"), to deal in the Software without restriction, including
   9  * without limitation the rights to use, copy, modify, merge, publish,
  10  * distribute, sub license, and/or sell copies of the Software, and to
  11  * permit persons to whom the Software is furnished to do so, subject to
  12  * the following conditions:
  13  *
  14  * The above copyright notice and this permission notice (including the
  15  * next paragraph) shall be included in all copies or substantial portions
  16  * of the Software.
  17  *
  18  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  19  * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  20  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT.
  21  * IN NO EVENT SHALL TUNGSTEN GRAPHICS AND/OR ITS SUPPLIERS BE LIABLE FOR
  22  * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
  23  * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
  24  * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  25  *
  26  **************************************************************************/
  27
  28 /**
  29  * \brief  polygon offset state
  30  *
  31  * \author  Keith Whitwell <keith@tungstengraphics.com>
  32  * \author  Brian Paul
  33  */
  34
  35 #include "pipe/p_util.h"
  36 #include "draw_private.h"
  37
  38
  39
  40 struct offset_stage {
  41    struct draw_stage stage;
  42
  43    float scale;
  44    float units;
  45 };
  46
  47
  48
  49 static INLINE struct offset_stage *offset_stage( struct draw_stage *stage )
  50 {
  51    return (struct offset_stage *) stage;
  52 }
  53
  54
  55 static void offset_begin( struct draw_stage *stage )
  56 {
  57    struct offset_stage *offset = offset_stage(stage);
  58    float mrd = 1.0f / 65535.0f; /* XXX this depends on depthbuffer bits! */
  59
  60    offset->units = stage->draw->setup.offset_units * mrd;
  61    offset->scale = stage->draw->setup.offset_scale;
  62
  63    stage->next->begin( stage->next );
  64 }
  65
  66
  67 /**
  68  * Offset tri Z.  Some hardware can handle this, but not usually when
  69  * doing unfilled rendering.
  70  */
  71 static void do_offset_tri( struct draw_stage *stage,
  72                            struct prim_header *header )
  73 {
  74    struct offset_stage *offset = offset_stage(stage);
  75    float inv_det = 1.0f / header->det;
  76
  77    /* Window coords:
  78     */
  79    float *v0 = header->v[0]->data[0];
  80    float *v1 = header->v[1]->data[0];
  81    float *v2 = header->v[2]->data[0];
  82
  83    /* edge vectors e = v0 - v2, f = v1 - v2 */
  84    float ex = v0[0] - v2[0];
  85    float ey = v0[1] - v2[1];
  86    float ez = v0[2] - v2[2];
  87    float fx = v1[0] - v2[0];
  88    float fy = v1[1] - v2[1];
  89    float fz = v1[2] - v2[2];
  90
  91    /* (a,b) = cross(e,f).xy */
  92    float a = ey*fz - ez*fy;
  93    float b = ez*fx - ex*fz;
  94
  95    float dzdx = FABSF(a * inv_det);
  96    float dzdy = FABSF(b * inv_det);
  97
  98    float zoffset = offset->units + MAX2(dzdx, dzdy) * offset->scale;
  99
 100    /*
 101     * Note: we're applying the offset and clamping per-vertex.
 102     * Ideally, the offset is applied per-fragment prior to fragment shading.
 103     */
 104    v0[2] = CLAMP(v0[2] + zoffset, 0.0f, 1.0f);
 105    v1[2] = CLAMP(v1[2] + zoffset, 0.0f, 1.0f);
 106    v2[2] = CLAMP(v2[2] + zoffset, 0.0f, 1.0f);
 107
 108    stage->next->tri( stage->next, header );
 109 }
 110
 111
 112 static void offset_tri( struct draw_stage *stage,
 113                         struct prim_header *header )
 114 {
 115    struct prim_header tmp;
 116
 117    tmp.det = header->det;
 118    tmp.v[0] = dup_vert(stage, header->v[0], 0);
 119    tmp.v[1] = dup_vert(stage, header->v[1], 1);
 120    tmp.v[2] = dup_vert(stage, header->v[2], 2);
 121
 122    do_offset_tri( stage, &tmp );
 123 }
 124
 125
 126
 127 static void offset_line( struct draw_stage *stage,
 128                        struct prim_header *header )
 129 {
 130    stage->next->line( stage->next, header );
 131 }
 132
 133
 134 static void offset_point( struct draw_stage *stage,
 135                         struct prim_header *header )
 136 {
 137    stage->next->point( stage->next, header );
 138 }
 139
 140
 141 static void offset_end( struct draw_stage *stage )
 142 {
 143    stage->next->end( stage->next );
 144 }
 145
 146
 147 static void offset_reset_stipple_counter( struct draw_stage *stage )
 148 {
 149    stage->next->reset_stipple_counter( stage->next );
 150 }
 151
 152
 153 /**
 154  * Create polygon offset drawing stage.
 155  */
 156 struct draw_stage *draw_offset_stage( struct draw_context *draw )
 157 {
 158    struct offset_stage *offset = CALLOC_STRUCT(offset_stage);
 159
 160    draw_alloc_tmps( &offset->stage, 3 );
 161
 162    offset->stage.draw = draw;
 163    offset->stage.next = NULL;
 164    offset->stage.begin = offset_begin;
 165    offset->stage.point = offset_point;
 166    offset->stage.line = offset_line;
 167    offset->stage.tri = offset_tri;
 168    offset->stage.end = offset_end;
 169    offset->stage.reset_stipple_counter = offset_reset_stipple_counter;
 170
 171    return &offset->stage;
 172 }