Home | History | Annotate | Download | only in draw 
      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  Drawing stage for polygon culling
     30  */
     31 
     32 /* Authors:  Keith Whitwell <keith (at) tungstengraphics.com>
     33  */
     34 
     35 
     36 #include "util/u_memory.h"
     37 #include "pipe/p_defines.h"
     38 #include "draw_pipe.h"
     39 
     40 
     41 struct cull_stage {
     42    struct draw_stage stage;
     43    unsigned cull_face;  /**< which face(s) to cull (one of PIPE_FACE_x) */
     44    unsigned front_ccw;
     45 };
     46 
     47 
     48 static INLINE struct cull_stage *cull_stage( struct draw_stage *stage )
     49 {
     50    return (struct cull_stage *)stage;
     51 }
     52 
     53 
     54 static void cull_tri( struct draw_stage *stage,
     55 		      struct prim_header *header )
     56 {
     57    const unsigned pos = draw_current_shader_position_output(stage->draw);
     58 
     59    /* Window coords: */
     60    const float *v0 = header->v[0]->data[pos];
     61    const float *v1 = header->v[1]->data[pos];
     62    const float *v2 = header->v[2]->data[pos];
     63 
     64    /* edge vectors: e = v0 - v2, f = v1 - v2 */
     65    const float ex = v0[0] - v2[0];
     66    const float ey = v0[1] - v2[1];
     67    const float fx = v1[0] - v2[0];
     68    const float fy = v1[1] - v2[1];
     69 
     70    /* det = cross(e,f).z */
     71    header->det = ex * fy - ey * fx;
     72 
     73    if (header->det != 0) {
     74       /* if det < 0 then Z points toward the camera and the triangle is
     75        * counter-clockwise winding.
     76        */
     77       unsigned ccw = (header->det < 0);
     78       unsigned face = ((ccw == cull_stage(stage)->front_ccw) ?
     79                        PIPE_FACE_FRONT :
     80                        PIPE_FACE_BACK);
     81 
     82       if ((face & cull_stage(stage)->cull_face) == 0) {
     83          /* triangle is not culled, pass to next stage */
     84 	 stage->next->tri( stage->next, header );
     85       }
     86    }
     87 }
     88 
     89 
     90 static void cull_first_tri( struct draw_stage *stage,
     91 			    struct prim_header *header )
     92 {
     93    struct cull_stage *cull = cull_stage(stage);
     94 
     95    cull->cull_face = stage->draw->rasterizer->cull_face;
     96    cull->front_ccw = stage->draw->rasterizer->front_ccw;
     97 
     98    stage->tri = cull_tri;
     99    stage->tri( stage, header );
    100 }
    101 
    102 
    103 static void cull_flush( struct draw_stage *stage, unsigned flags )
    104 {
    105    stage->tri = cull_first_tri;
    106    stage->next->flush( stage->next, flags );
    107 }
    108 
    109 
    110 static void cull_reset_stipple_counter( struct draw_stage *stage )
    111 {
    112    stage->next->reset_stipple_counter( stage->next );
    113 }
    114 
    115 
    116 static void cull_destroy( struct draw_stage *stage )
    117 {
    118    draw_free_temp_verts( stage );
    119    FREE( stage );
    120 }
    121 
    122 
    123 /**
    124  * Create a new polygon culling stage.
    125  */
    126 struct draw_stage *draw_cull_stage( struct draw_context *draw )
    127 {
    128    struct cull_stage *cull = CALLOC_STRUCT(cull_stage);
    129    if (cull == NULL)
    130       goto fail;
    131 
    132    cull->stage.draw = draw;
    133    cull->stage.name = "cull";
    134    cull->stage.next = NULL;
    135    cull->stage.point = draw_pipe_passthrough_point;
    136    cull->stage.line = draw_pipe_passthrough_line;
    137    cull->stage.tri = cull_first_tri;
    138    cull->stage.flush = cull_flush;
    139    cull->stage.reset_stipple_counter = cull_reset_stipple_counter;
    140    cull->stage.destroy = cull_destroy;
    141 
    142    if (!draw_alloc_temp_verts( &cull->stage, 0 ))
    143       goto fail;
    144 
    145    return &cull->stage;
    146 
    147 fail:
    148    if (cull)
    149       cull->stage.destroy( &cull->stage );
    150 
    151    return NULL;
    152 }
    153