Attachment 107103 Details for Bug 84396 – Fix loss of precision from projection onto sample grid

[patch] Fix loss of precision from projection onto sample grid

0001-tor-Fix-loss-of-precision-from-projection-onto-sampl.patch (text/plain), 13.42 KB, created by Chris Wilson on 2014-09-30 08:09:23 UTC

(hide)

Description:

Filename:

MIME Type:

Creator: Chris Wilson

Created: 2014-09-30 08:09:23 UTC

Size: 13.42 KB

patch

obsolete

>From af84af36eaf6ef1b49e80c286e1ea79aa1004ffb Mon Sep 17 00:00:00 2001
>From: Chris Wilson <chris@chris-wilson.co.uk>
>Date: Tue, 30 Sep 2014 08:44:43 +0100
>Subject: [PATCH] tor: Fix loss of precision from projection onto sample grid
>
>The goal is to preserve the precision in the gradients of the edges and
>only apply the projection into the final cell location. We also include
>the half-subrow offset as spotted by Massimo.
>
>References: https://bugs.freedesktop.org/show_bug.cgi?id=84396
>Testcase: coverage-rhombus
>Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
>---
> src/cairo-tor-scan-converter.c | 317 +++++++++++++++++++++--------------------
> 1 file changed, 164 insertions(+), 153 deletions(-)
>
>diff --git a/src/cairo-tor-scan-converter.c b/src/cairo-tor-scan-converter.c
>index 89ef20f..2b81fe5 100644
>--- a/src/cairo-tor-scan-converter.c
>+++ b/src/cairo-tor-scan-converter.c
>@@ -315,7 +315,7 @@ struct edge {
>     /* Original sign of the edge: +1 for downwards, -1 for upwards
>      * edges.  */
>     int dir;
>-    int vertical;
>+    int cell;
> 
>     /* Current x coordinate while the edge is on the active
>      * list. Initialised to the x coordinate of the top of the
>@@ -473,22 +473,6 @@ floored_divrem(int a, int b)
>     return qr;
> }
> 
>-/* Compute the floored division (x*a)/b. Assumes / and % perform symmetric
>- * division. */
>-static struct quorem
>-floored_muldivrem(int x, int a, int b)
>-{
>-    struct quorem qr;
>-    long long xa = (long long)x*a;
>-    qr.quo = xa/b;
>-    qr.rem = xa%b;
>-    if ((xa>=0) != (b>=0) && qr.rem) {
>-	qr.quo -= 1;
>-	qr.rem += b;
>-    }
>-    return qr;
>-}
>-
> static struct _pool_chunk *
> _pool_chunk_init(
>     struct _pool_chunk *p,
>@@ -778,6 +762,26 @@ cell_list_add_subspan(struct cell_list *cells,
>     }
> }
> 
>+inline static void full_step (struct edge *e)
>+{
>+    if (e->dy == 0)
>+	return;
>+
>+    e->x.quo += e->dxdy_full.quo;
>+    e->x.rem += e->dxdy_full.rem;
>+    if (e->x.rem < 0) {
>+	e->x.quo--;
>+	e->x.rem += e->dy;
>+    } else if (e->x.rem >= e->dy) {
>+	++e->x.quo;
>+	e->x.rem -= e->dy;
>+    }
>+    assert (e->x.rem >= 0 && e->x.rem < e->dy);
>+
>+    e->cell = e->x.quo + (e->x.rem >= e->dy/2);
>+}
>+
>+
> /* Adds the analytical coverage of an edge crossing the current pixel
>  * row to the coverage cells and advances the edge's x position to the
>  * following row.
>@@ -805,22 +809,14 @@ cell_list_render_edge(struct cell_list *cells,
>     int ix1, ix2;
>     grid_scaled_x_t fx1, fx2;
> 
>-    struct quorem x1 = edge->x;
>-    struct quorem x2 = x1;
>+    int x1, x2;
> 
>-    if (! edge->vertical) {
>-	x2.quo += edge->dxdy_full.quo;
>-	x2.rem += edge->dxdy_full.rem;
>-	if (x2.rem >= 0) {
>-	    ++x2.quo;
>-	    x2.rem -= edge->dy;
>-	}
>+    x1 = edge->cell;
>+    full_step (edge);
>+    x2 = edge->cell;
> 
>-	edge->x = x2;
>-    }
>-
>-    GRID_X_TO_INT_FRAC(x1.quo, ix1, fx1);
>-    GRID_X_TO_INT_FRAC(x2.quo, ix2, fx2);
>+    GRID_X_TO_INT_FRAC(x1, ix1, fx1);
>+    GRID_X_TO_INT_FRAC(x2, ix2, fx2);
> 
>     /* Edge is entirely within a column? */
>     if (ix1 == ix2) {
>@@ -833,7 +829,7 @@ cell_list_render_edge(struct cell_list *cells,
>     }
> 
>     /* Orient the edge left-to-right. */
>-    dx = x2.quo - x1.quo;
>+    dx = x2 - x1;
>     if (dx >= 0) {
> 	y1 = 0;
> 	y2 = GRID_Y;
>@@ -976,78 +972,19 @@ _polygon_insert_edge_into_its_y_bucket(struct polygon *polygon,
>     *ptail = e;
> }
> 
>-inline static void
>-polygon_add_edge (struct polygon *polygon,
>-		  const cairo_edge_t *edge)
>-{
>-    struct edge *e;
>-    grid_scaled_x_t dx;
>-    grid_scaled_y_t dy;
>-    grid_scaled_y_t ytop, ybot;
>-    grid_scaled_y_t ymin = polygon->ymin;
>-    grid_scaled_y_t ymax = polygon->ymax;
>-
>-    if (unlikely (edge->top >= ymax || edge->bottom <= ymin))
>-	return;
>-
>-    e = pool_alloc (polygon->edge_pool.base, sizeof (struct edge));
>-
>-    dx = edge->line.p2.x - edge->line.p1.x;
>-    dy = edge->line.p2.y - edge->line.p1.y;
>-    e->dy = dy;
>-    e->dir = edge->dir;
>-
>-    ytop = edge->top >= ymin ? edge->top : ymin;
>-    ybot = edge->bottom <= ymax ? edge->bottom : ymax;
>-    e->ytop = ytop;
>-    e->height_left = ybot - ytop;
>-
>-    if (dx == 0) {
>-	e->vertical = TRUE;
>-	e->x.quo = edge->line.p1.x;
>-	e->x.rem = 0;
>-	e->dxdy.quo = 0;
>-	e->dxdy.rem = 0;
>-	e->dxdy_full.quo = 0;
>-	e->dxdy_full.rem = 0;
>-    } else {
>-	e->vertical = FALSE;
>-	e->dxdy = floored_divrem (dx, dy);
>-	if (ytop == edge->line.p1.y) {
>-	    e->x.quo = edge->line.p1.x;
>-	    e->x.rem = 0;
>-	} else {
>-	    e->x = floored_muldivrem (ytop - edge->line.p1.y, dx, dy);
>-	    e->x.quo += edge->line.p1.x;
>-	}
>-
>-	if (e->height_left >= GRID_Y) {
>-	    e->dxdy_full = floored_muldivrem (GRID_Y, dx, dy);
>-	} else {
>-	    e->dxdy_full.quo = 0;
>-	    e->dxdy_full.rem = 0;
>-	}
>-    }
>-
>-    _polygon_insert_edge_into_its_y_bucket (polygon, e);
>-
>-    e->x.rem -= dy;		/* Bias the remainder for faster
>-				 * edge advancement. */
>-}
>-
> static void
> active_list_reset (struct active_list *active)
> {
>-    active->head.vertical = 1;
>     active->head.height_left = INT_MAX;
>-    active->head.x.quo = INT_MIN;
>+    active->head.dy = 0;
>+    active->head.cell = INT_MIN;
>     active->head.prev = NULL;
>     active->head.next = &active->tail;
>     active->tail.prev = &active->head;
>     active->tail.next = NULL;
>-    active->tail.x.quo = INT_MAX;
>+    active->tail.cell = INT_MAX;
>     active->tail.height_left = INT_MAX;
>-    active->tail.vertical = 1;
>+    active->tail.dy = 0;
>     active->min_height = 0;
>     active->is_vertical = 1;
> }
>@@ -1084,7 +1021,7 @@ merge_sorted_edges (struct edge *head_a, struct edge *head_b)
> 
>     prev = head_a->prev;
>     next = &head;
>-    if (head_a->x.quo <= head_b->x.quo) {
>+    if (head_a->cell <= head_b->cell) {
> 	head = head_a;
>     } else {
> 	head = head_b;
>@@ -1093,8 +1030,8 @@ merge_sorted_edges (struct edge *head_a, struct edge *head_b)
>     }
> 
>     do {
>-	x = head_b->x.quo;
>-	while (head_a != NULL && head_a->x.quo <= x) {
>+	x = head_b->cell;
>+	while (head_a != NULL && head_a->cell <= x) {
> 	    prev = head_a;
> 	    next = &head_a->next;
> 	    head_a = head_a->next;
>@@ -1106,8 +1043,8 @@ merge_sorted_edges (struct edge *head_a, struct edge *head_b)
> 	    return head;
> 
> start_with_b:
>-	x = head_a->x.quo;
>-	while (head_b != NULL && head_b->x.quo <= x) {
>+	x = head_a->cell;
>+	while (head_b != NULL && head_b->cell <= x) {
> 	    prev = head_b;
> 	    next = &head_b->next;
> 	    head_b = head_b->next;
>@@ -1153,7 +1090,7 @@ sort_edges (struct edge *list,
>     }
> 
>     remaining = head_other->next;
>-    if (list->x.quo <= head_other->x.quo) {
>+    if (list->cell <= head_other->cell) {
> 	*head_out = list;
> 	head_other->next = NULL;
>     } else {
>@@ -1197,7 +1134,7 @@ can_do_full_row (struct active_list *active)
> 	while (NULL != e) {
> 	    if (e->height_left < min_height)
> 		min_height = e->height_left;
>-	    is_vertical &= e->vertical;
>+	    is_vertical &= e->dy == 0;
> 	    e = e->next;
> 	}
> 
>@@ -1210,19 +1147,27 @@ can_do_full_row (struct active_list *active)
> 
>     /* Check for intersections as no edges end during the next row. */
>     for (e = active->head.next; e != &active->tail; e = e->next) {
>-	struct quorem x = e->x;
>+	int cell;
> 
>-	if (! e->vertical) {
>+	if (e->dy) {
>+	    struct quorem x = e->x;
> 	    x.quo += e->dxdy_full.quo;
> 	    x.rem += e->dxdy_full.rem;
>-	    if (x.rem >= 0)
>-		++x.quo;
>-	}
>+	    if (x.rem < 0) {
>+		x.quo--;
>+		x.rem += e->dy;
>+	    } else if (x.rem >= e->dy) {
>+		x.quo++;
>+		x.rem -= e->dy;
>+	    }
>+	    cell = x.quo + (x.rem >= e->dy/2);
>+	} else
>+	    cell = e->cell;
> 
>-	if (x.quo < prev_x)
>+	if (cell < prev_x)
> 	    return 0;
> 
>-	prev_x = x.quo;
>+	prev_x = cell;
>     }
> 
>     return 1;
>@@ -1256,7 +1201,7 @@ polygon_fill_buckets (struct active_list *active,
> 	buckets[suby] = edge;
> 	if (edge->height_left < min_height)
> 	    min_height = edge->height_left;
>-	is_vertical &= edge->vertical;
>+	is_vertical &= edge->dy == 0;
> 	edge = next;
>     }
> 
>@@ -1264,6 +1209,25 @@ polygon_fill_buckets (struct active_list *active,
>     active->min_height = min_height;
> }
> 
>+static void step (struct edge *edge)
>+{
>+    if (edge->dy == 0)
>+	return;
>+
>+    edge->x.quo += edge->dxdy.quo;
>+    edge->x.rem += edge->dxdy.rem;
>+    if (edge->x.rem < 0) {
>+	--edge->x.quo;
>+	edge->x.rem += edge->dy;
>+    } else if (edge->x.rem >= edge->dy) {
>+	++edge->x.quo;
>+	edge->x.rem -= edge->dy;
>+    }
>+    assert (edge->x.rem >= 0 && edge->x.rem < edge->dy);
>+
>+    edge->cell = edge->x.quo + (edge->x.rem >= edge->dy/2);
>+}
>+
> inline static void
> sub_row (struct active_list *active,
> 	 struct cell_list *coverages,
>@@ -1277,29 +1241,24 @@ sub_row (struct active_list *active,
> 
>     while (&active->tail != edge) {
> 	struct edge *next = edge->next;
>-	int xend = edge->x.quo;
>+	int xend = edge->cell;
> 
> 	if (--edge->height_left) {
>-	    edge->x.quo += edge->dxdy.quo;
>-	    edge->x.rem += edge->dxdy.rem;
>-	    if (edge->x.rem >= 0) {
>-		++edge->x.quo;
>-		edge->x.rem -= edge->dy;
>-	    }
>+	    step (edge);
> 
>-	    if (edge->x.quo < prev_x) {
>+	    if (edge->cell < prev_x) {
> 		struct edge *pos = edge->prev;
> 		pos->next = next;
> 		next->prev = pos;
> 		do {
> 		    pos = pos->prev;
>-		} while (edge->x.quo < pos->x.quo);
>+		} while (edge->cell < pos->cell);
> 		pos->next->prev = edge;
> 		edge->next = pos->next;
> 		edge->prev = pos;
> 		pos->next = edge;
> 	    } else
>-		prev_x = edge->x.quo;
>+		prev_x = edge->cell;
> 	    active->min_height = -1;
> 	} else {
> 	    edge->prev->next = next;
>@@ -1308,7 +1267,7 @@ sub_row (struct active_list *active,
> 
> 	winding += edge->dir;
> 	if ((winding & mask) == 0) {
>-	    if (next->x.quo != xend) {
>+	    if (next->cell != xend) {
> 		cell_list_add_subspan (coverages, xstart, xend);
> 		xstart = INT_MIN;
> 	    }
>@@ -1329,18 +1288,6 @@ inline static void dec (struct active_list *a, struct edge *e, int h)
>     }
> }
> 
>-inline static void full_step (struct edge *e)
>-{
>-    if (! e->vertical) {
>-	e->x.quo += e->dxdy_full.quo;
>-	e->x.rem += e->dxdy_full.rem;
>-	if (e->x.rem >= 0) {
>-	    ++e->x.quo;
>-	    e->x.rem -= e->dy;
>-	}
>-    }
>-}
>-
> static void
> full_row (struct active_list *active,
> 	  struct cell_list *coverages,
>@@ -1360,7 +1307,7 @@ full_row (struct active_list *active,
> 	    dec (active, right, GRID_Y);
> 
> 	    winding += right->dir;
>-	    if ((winding & mask) == 0 && right->next->x.quo != right->x.quo)
>+	    if ((winding & mask) == 0 && right->next->cell != right->cell)
> 		break;
> 
> 	    full_step (right);
>@@ -1482,10 +1429,92 @@ glitter_scan_converter_reset(
> 
> #define INPUT_TO_GRID_general(in, out, grid_scale) do {		\
>     long long tmp__ = (long long)(grid_scale) * (in);	\
>+    tmp__ += 1 << (GLITTER_INPUT_BITS-1);			\
>     tmp__ >>= GLITTER_INPUT_BITS;				\
>     (out) = tmp__;						\
> } while (0)
> 
>+inline static void
>+polygon_add_edge (struct polygon *polygon,
>+		  const cairo_edge_t *edge)
>+{
>+    struct edge *e;
>+    grid_scaled_y_t ytop, ybot;
>+    const cairo_point_t *p1, *p2;
>+
>+    INPUT_TO_GRID_Y (edge->top, ytop);
>+    if (ytop < polygon->ymin)
>+	    ytop = polygon->ymin;
>+
>+    INPUT_TO_GRID_Y (edge->bottom, ybot);
>+    if (ybot > polygon->ymax)
>+	    ybot = polygon->ymax;
>+
>+    if (ybot <= ytop)
>+	    return;
>+
>+    e = pool_alloc (polygon->edge_pool.base, sizeof (struct edge));
>+
>+    e->ytop = ytop;
>+    e->height_left = ybot - ytop;
>+    if (edge->line.p2.y > edge->line.p1.y) {
>+	    e->dir = edge->dir;
>+	    p1 = &edge->line.p1;
>+	    p2 = &edge->line.p2;
>+    } else {
>+	    e->dir = -edge->dir;
>+	    p1 = &edge->line.p2;
>+	    p2 = &edge->line.p1;
>+    }
>+
>+    if (p2->x == p1->x) {
>+	e->cell = p1->x;
>+	e->x.quo = e->x.rem = 0;
>+	e->dxdy.quo = e->dxdy.rem = 0;
>+	e->dxdy_full.quo = e->dxdy_full.rem = 0;
>+	e->dy = 0;
>+    } else {
>+	int64_t Ex, Ey, tmp;
>+
>+	Ex = (int64_t)(p2->x - p1->x) * GRID_X;
>+	Ey = (int64_t)(p2->y - p1->y) * GRID_Y * (2 << GLITTER_INPUT_BITS);
>+
>+	e->dxdy.quo = Ex * (2 << GLITTER_INPUT_BITS) / Ey;
>+	e->dxdy.rem = Ex * (2 << GLITTER_INPUT_BITS) % Ey;
>+
>+	tmp = (int64_t)(2*ytop + 1) << GLITTER_INPUT_BITS;
>+	tmp -= (int64_t)p1->y * GRID_Y * 2;
>+	tmp *= Ex;
>+	e->x.quo = tmp / Ey;
>+	e->x.rem = tmp % Ey;
>+
>+	tmp = (int64_t)p1->x * GRID_X;
>+	e->x.quo += tmp >> GLITTER_INPUT_BITS;
>+	e->x.rem += ((tmp & ((1 << GLITTER_INPUT_BITS) - 1)) * Ey) / (1 << GLITTER_INPUT_BITS);
>+
>+	if (e->x.rem < 0) {
>+		e->x.quo--;
>+		e->x.rem += Ey;
>+	} else  if (e->x.rem >= Ey) {
>+		e->x.quo++;
>+		e->x.rem -= Ey;
>+	}
>+	assert (e->x.rem >= 0 && e->x.rem < Ey);
>+
>+	if (e->height_left >= GRID_Y) {
>+	    tmp = Ex * (2 * GRID_Y << GLITTER_INPUT_BITS);
>+	    e->dxdy_full.quo = tmp / Ey;
>+	    e->dxdy_full.rem = tmp % Ey;
>+	} else
>+	    e->dxdy_full.quo = e->dxdy_full.rem = 0;
>+
>+	e->cell = e->x.quo + (e->x.rem >= Ey/2);
>+	e->dy = Ey;
>+    }
>+
>+    _polygon_insert_edge_into_its_y_bucket (polygon, e);
>+}
>+
> /* Add a new polygon edge from pixel (x1,y1) to (x2,y2) to the scan
>  * converter.  The coordinates represent pixel positions scaled by
>  * 2**GLITTER_PIXEL_BITS.  If this function fails then the scan
>@@ -1495,25 +1524,7 @@ I void
> glitter_scan_converter_add_edge (glitter_scan_converter_t *converter,
> 				 const cairo_edge_t *edge)
> {
>-    cairo_edge_t e;
>-
>-    INPUT_TO_GRID_Y (edge->top, e.top);
>-    INPUT_TO_GRID_Y (edge->bottom, e.bottom);
>-    if (e.top >= e.bottom)
>-	return;
>-
>-    /* XXX: possible overflows if GRID_X/Y > 2**GLITTER_INPUT_BITS */
>-    INPUT_TO_GRID_Y (edge->line.p1.y, e.line.p1.y);
>-    INPUT_TO_GRID_Y (edge->line.p2.y, e.line.p2.y);
>-    if (e.line.p1.y == e.line.p2.y)
>-	e.line.p2.y++; /* little fudge to prevent a div-by-zero */
>-
>-    INPUT_TO_GRID_X (edge->line.p1.x, e.line.p1.x);
>-    INPUT_TO_GRID_X (edge->line.p2.x, e.line.p2.x);
>-
>-    e.dir = edge->dir;
>-
>-    polygon_add_edge (converter->polygon, &e);
>+    polygon_add_edge (converter->polygon, edge);
> }
> 
> static void
>-- 
>2.1.1
>

Actions: View | Splinter Review

Attachments on bug 84396: 106961 | 106989 | 107095 | 107101 | 107103 | 107104 | 107186 | 107189 | 107344

Use of freedesktop.org services, including Bugzilla, is subject to our Code of Conduct. How we collect and use information is described in our Privacy Policy.