Fix a bug for trapezoid clip

 We find in some cases the trapezoid will be render as a triangle and
 the left edge and right edge will cross with each other just bellow
 the top or over the bottom. The distance between the cross poind and
 the top or bottom is less than pixman_fixed_1_minus_e, so after the
 fixed converted to int, the cross point has the same value with the
 top or botton and the triangle should not be affected. But in our
 clip logic, the cross point will be clipped out. So add a logic
 to fix this problem.

Signed-off-by: Junyan He <junyan.he@linux.intel.com>

1 files changed, 107 insertions, 8 deletions

diff --git a/src/glamor_trapezoid.c b/src/glamor_trapezoid.c
index cc6a706..3ad9e50 100644
--- a/src/glamor_trapezoid.c
+++ b/src/glamor_trapezoid.c
@@ -38,6 +38,8 @@
 
 #ifdef GLAMOR_TRAPEZOID_SHADER
 
+#define DEBUG_CLIP_VTX 0
+
 #define POINT_INSIDE_CLIP_RECT(point, rect)	\
     (point[0] >= IntToxFixed(rect->x1)		\
      && point[0] <= IntToxFixed(rect->x2) 	\
@@ -45,6 +47,28 @@
      && point[1] <= IntToxFixed(rect->y2))
 
 static xFixed
+_glamor_lines_crossfixedY (xLineFixed *l, xLineFixed *r)
+{
+	xFixed dx1 = l->p2.x - l->p1.x;
+	xFixed dx2 = r->p2.x - r->p1.x;
+	xFixed dy1 = l->p2.y - l->p1.y;
+	xFixed dy2 = r->p2.y - r->p1.y;
+	xFixed_32_32 tmp = (xFixed_32_32) dy2 * dy1;
+	xFixed_32_32 dividend1 = (tmp >> 32) * (l->p1.x - r->p1.x);
+	tmp = (xFixed_32_32) dx1 * dy2;
+	xFixed_32_32 dividend2 = (tmp >> 32) * l->p1.y;
+	tmp = (xFixed_32_32) dy1 * dx2;
+	xFixed_32_32 dividend3 = (tmp >> 32) * r->p1.y;
+	xFixed_32_32 divisor = ((xFixed_32_32) dx1 * (xFixed_32_32) dy2
+	                           - (xFixed_32_32) dy1 * (xFixed_32_32) dx2) >> 32;
+
+	if (divisor)
+		return (xFixed)((dividend2 - dividend1 - dividend3) / divisor);
+
+	return 0xFFFFFFFF;
+}
+
+static xFixed
 _glamor_linefixedX (xLineFixed *l, xFixed y, Bool ceil)
 {
 	xFixed dx = l->p2.x - l->p1.x;
@@ -67,22 +91,86 @@ _glamor_linefixedY (xLineFixed *l, xFixed x, Bool ceil)
 }
 
 static Bool
-point_inside_trapezoid(int point[2], xTrapezoid * trap)
+point_inside_trapezoid(int point[2], xTrapezoid * trap, xFixed cut_y)
 {
 	int ret = TRUE;
 	int tmp;
-	if (point[1] > trap->bottom
-	     || point[1] < trap->top)
+	if (point[1] > trap->bottom) {
 		ret = FALSE;
+		if (DEBUG_CLIP_VTX) {
+			ErrorF("Out of Trap bottom, point[1] = %d(0x%x)), "
+			       "bottom = %d(0x%x)\n",
+			       (unsigned int)xFixedToInt(point[1]), point[1],
+			       (unsigned int)xFixedToInt(trap->bottom),
+			       (unsigned int)trap->bottom);
+		}
+
+		return ret;
+	}
+
+	if (point[1] < trap->top) {
+		ret = FALSE;
+		if (DEBUG_CLIP_VTX) {
+			ErrorF("Out of Trap top, point[1] = %d(0x%x)), "
+			     "top = %d(0x%x)\n",
+			     (unsigned int)xFixedToInt(point[1]), point[1],
+			     (unsigned int)xFixedToInt(trap->top),
+			     (unsigned int)trap->top);
+		}
+
+		return ret;
+	}
 
 	tmp = _glamor_linefixedX (&trap->left, point[1], FALSE);
-	if (point[0] < tmp)
+	if (point[0] < tmp) {
 		ret = FALSE;
 
+		if (abs(cut_y - trap->top) < pixman_fixed_1_minus_e &&
+		           abs(point[1] - trap->top) < pixman_fixed_1_minus_e &&
+		           tmp - point[0] < pixman_fixed_1_minus_e) {
+			ret = TRUE;
+		} else if (abs(cut_y - trap->bottom) < pixman_fixed_1_minus_e &&
+		           point[1] - trap->bottom < pixman_fixed_1_minus_e &&
+		           tmp - point[0] < pixman_fixed_1_minus_e) {
+			ret = TRUE;
+		}
+
+		if (DEBUG_CLIP_VTX && !ret) {
+			ErrorF("Out of Trap left, point[0] = %d(0x%x)), "
+			       "left = %d(0x%x)\n",
+			       (unsigned int)xFixedToInt(point[0]), point[0],
+			       (unsigned int)xFixedToInt(tmp), (unsigned int)tmp);
+		}
+
+		if (!ret)
+			return ret;
+	}
+
 	tmp = _glamor_linefixedX (&trap->right, point[1], TRUE);
-	if (point[0] > tmp)
+	if (point[0] > tmp) {
 		ret = FALSE;
 
+		if (abs(cut_y - trap->top) < pixman_fixed_1_minus_e &&
+		           abs(point[1] - trap->top) < pixman_fixed_1_minus_e &&
+		           point[0] - tmp < pixman_fixed_1_minus_e) {
+			ret = TRUE;
+		} else if (abs(cut_y - trap->bottom) < pixman_fixed_1_minus_e &&
+		           abs(point[1] - trap->bottom) < pixman_fixed_1_minus_e &&
+		           point[0] - tmp < pixman_fixed_1_minus_e) {
+			ret = TRUE;
+		}
+
+		if (DEBUG_CLIP_VTX && !ret) {
+			ErrorF("Out of Trap right, point[0] = %d(0x%x)), "
+			       "right = %d(0x%x)\n",
+			       (unsigned int)xFixedToInt(point[0]), point[0],
+			       (unsigned int)xFixedToInt(tmp), (unsigned int)tmp);
+		}
+
+		if (!ret)
+			return ret;
+	}
+
 	return ret;
 }
 
@@ -125,12 +213,11 @@ glamor_flush_composite_triangles(ScreenPtr screen)
 	glamor_put_dispatch(glamor_priv);
 }
 
-#define DEBUG_CLIP_VTX 0
-
 static Bool
 _glamor_clip_trapezoid_vertex(xTrapezoid * trap, BoxPtr pbox,
         int vertex[6], int *num)
 {
+	xFixed edge_cross_y = 0xFFFFFFFF;
 	int tl[2];
 	int bl[2];
 	int tr[2];
@@ -217,7 +304,7 @@ _glamor_clip_trapezoid_vertex(xTrapezoid * trap, BoxPtr pbox,
 
 #define ADD_VERTEX_IF_INSIDE(vtx)				\
 	if(POINT_INSIDE_CLIP_RECT(vtx, pbox)			\
-	   && point_inside_trapezoid(vtx, trap)){		\
+	   && point_inside_trapezoid(vtx, trap, edge_cross_y)){	\
 	    tmp_vtx[vertex_num] = xFixedToInt(vtx[0]);		\
 	    tmp_vtx[vertex_num + 1] = xFixedToInt(vtx[1]);	\
 	    vertex_num += 2;					\
@@ -239,6 +326,18 @@ _glamor_clip_trapezoid_vertex(xTrapezoid * trap, BoxPtr pbox,
 		       "the Rect\n");				\
 	}
 
+	/*Trap's right edge cut right edge. */
+	if((!IS_TRAP_EDGE_VERTICAL((&trap->left))) ||
+	        (!IS_TRAP_EDGE_VERTICAL((&trap->right)))) {
+		edge_cross_y = _glamor_lines_crossfixedY((&trap->left), (&trap->right));
+		if (DEBUG_CLIP_VTX) {
+			ErrorF("Trap's left edge cut right edge at %d(0x%x), "
+			       "trap_top = %x, trap_bottom = %x\n",
+			       xFixedToInt(edge_cross_y), edge_cross_y,
+			       (unsigned int)trap->top, (unsigned int)trap->bottom);
+		}
+	}
+
 	/*Trap's TopLeft, BottomLeft, TopRight and BottomRight. */
 	CACULATE_CUT_VERTEX(tl, 1, FALSE, trap->top, (&trap->left));
 	CACULATE_CUT_VERTEX(bl, 1, FALSE, trap->bottom, (&trap->left));