122 lines
2.9 KiB
PHP
122 lines
2.9 KiB
PHP
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#define CLIP_TOP 1
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#define CLIP_BOTTOM 2
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#define CLIP_RIGHT 4
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#define CLIP_LEFT 8
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typedef struct
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{
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int xmin;
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int ymin;
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int xmax;
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int ymax;
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}clip_t;
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static int _L1OutCode( clip_t *clip, int x, int y )
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/*=================================
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Verify that a point is inside or outside the active viewport. */
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{
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int flag;
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flag = 0;
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if( x < clip->xmin ) {
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flag |= CLIP_LEFT;
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} else if( x > clip->xmax ) {
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flag |= CLIP_RIGHT;
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}
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if( y < clip->ymin ) {
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flag |= CLIP_TOP;
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} else if( y > clip->ymax ) {
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flag |= CLIP_BOTTOM;
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}
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return( flag );
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};
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static void block_inter( clip_t *clip, int *x, int *y, int flag )
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/*======================================================
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Find the intersection of a block with a boundary of the viewport. */
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{
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if( flag & CLIP_TOP ) {
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*y = clip->ymin;
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} else if( flag & CLIP_BOTTOM ) {
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*y = clip->ymax;
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} else if( flag & CLIP_RIGHT ) {
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*x = clip->xmax;
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} else if( flag & CLIP_LEFT ) {
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*x = clip->xmin;
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}
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}
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int BlockClip(clip_t *clip, int *x1, int *y1, int *x2, int* y2 )
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/*==============================================================
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Clip a block with opposite corners (x1,y1) and (x2,y2) to the
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active viewport based on the Cohen-Sutherland algorithm for line
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clipping. Return the clipped coordinates and a decision drawing
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flag ( 0 draw : 1 don't draw ). */
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{
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int flag1;
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int flag2;
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flag1 = _L1OutCode( clip, *x1, *y1 );
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flag2 = _L1OutCode( clip, *x2, *y2 );
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for( ;; ) {
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if( flag1 & flag2 ) break; /* trivially outside */
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if( flag1 == flag2 ) break; /* completely inside */
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if( flag1 == 0 ) {
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block_inter( clip, x2, y2, flag2 );
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flag2 = _L1OutCode( clip, *x2, *y2 );
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} else {
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block_inter( clip, x1, y1, flag1 );
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flag1 = _L1OutCode( clip, *x1, *y1 );
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}
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}
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return( flag1 & flag2 );
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}
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int blit_clip(clip_t *dst_clip,int *dst_x,int *dst_y,
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clip_t *src_clip,int *src_x, int *src_y,
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u32_t *w, u32_t *h)
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{
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int sx0, sy0, sx1, sy1;
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sx0 = *src_x;
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sy0 = *src_y;
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sx1 = sx0 + *w - 1;
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sy1 = sy0 + *h - 1;
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if( ! BlockClip( src_clip, &sx0, &sy0, &sx1, &sy1))
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{
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int dx0, dy0, dx1, dy1;
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dx0 = *dst_x + sx0 - *src_x;
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dy0 = *dst_y + sy0 - *src_y;
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dx1 = dx0 + sx1 - sx0;
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dy1 = dy0 + sy1 - sy0;
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if( ! BlockClip( dst_clip, &dx0, &dy0, &dx1, &dy1))
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{
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*w = dx1 - dx0 + 1;
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*h = dy1 - dy0 + 1;
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*src_x += dx0 - *dst_x;
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*src_y += dy0 - *dst_y;
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*dst_x = dx0;
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*dst_y = dy0;
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return 0;
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};
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}
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return 1;
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};
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