compositor: rewrite draw and input coordinate transformations

For unifying the coordinate system handling, introduce functions for
converting explicitly between the global and the surface local
coordinate systems.

Use these functions in the input path, replacing
weston_surface_transform().

In the draw path, rewrite transform_vertex() to take in surface local
coordinates.

As shell now uses the new functions, the rotation origin is properly
placed in the middle of the surface.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>

3 files changed, 97 insertions, 49 deletions

diff --git a/src/compositor.c b/src/compositor.c
index 3330ffb..cc77747 100644
--- a/src/compositor.c
+++ b/src/compositor.c
@@ -259,6 +259,65 @@ weston_surface_update_transform(struct weston_surface *surface)
 }
 
 WL_EXPORT void
+weston_surface_to_global(struct weston_surface *surface,
+			 int32_t sx, int32_t sy, int32_t *x, int32_t *y)
+{
+	weston_surface_update_transform(surface);
+
+	if (surface->transform.enabled) {
+		struct weston_vector v = { { sx, sy, 0.0f, 1.0f } };
+
+		v.f[0] += surface->x;
+		v.f[1] += surface->y;
+
+		weston_matrix_transform(&surface->transform.matrix, &v);
+
+		if (fabsf(v.f[3]) < 1e-6) {
+			fprintf(stderr, "warning: numerical instability in "
+				"weston_surface_to_global(), divisor = %g\n",
+				v.f[3]);
+			*x = 0;
+			*y = 0;
+			return;
+		}
+
+		*x = floorf(v.f[0] / v.f[3]);
+		*y = floorf(v.f[1] / v.f[3]);
+	} else {
+		*x = sx + surface->x;
+		*y = sy + surface->y;
+	}
+}
+
+WL_EXPORT void
+weston_surface_from_global(struct weston_surface *surface,
+			   int32_t x, int32_t y, int32_t *sx, int32_t *sy)
+{
+	weston_surface_update_transform(surface);
+
+	if (surface->transform.enabled) {
+		struct weston_vector v = { { x, y, 0.0f, 1.0f } };
+
+		weston_matrix_transform(&surface->transform.inverse, &v);
+
+		if (fabsf(v.f[3]) < 1e-6) {
+			fprintf(stderr, "warning: numerical instability in "
+				"weston_surface_from_global(), divisor = %g\n",
+				v.f[3]);
+			*sx = 0;
+			*sy = 0;
+			return;
+		}
+
+		*sx = floorf(v.f[0] / v.f[3] - surface->x);
+		*sy = floorf(v.f[1] / v.f[3] - surface->y);
+	} else {
+		*sx = x - surface->x;
+		*sy = y - surface->y;
+	}
+}
+
+WL_EXPORT void
 weston_surface_damage_rectangle(struct weston_surface *surface,
 			      int32_t x, int32_t y,
 			      int32_t width, int32_t height)
@@ -337,23 +396,6 @@ weston_surface_configure(struct weston_surface *surface,
 		pixman_region32_init(&surface->opaque);
 }
 
-static void
-weston_surface_transform(struct weston_surface *surface,
-		       int32_t x, int32_t y, int32_t *sx, int32_t *sy)
-{
-	weston_surface_update_transform(surface);
-
-	if (surface->transform.enabled) {
-		struct weston_vector v = { { x, y, 0.0f, 1.0f } };
-		weston_matrix_transform(&surface->transform.inverse, &v);
-		x = floorf(v.f[0] / v.f[3]);
-		y = floorf(v.f[1] / v.f[3]);
-	}
-
-	*sx = x - surface->x;
-	*sy = y - surface->y;
-}
-
 WL_EXPORT uint32_t
 weston_compositor_get_time(void)
 {
@@ -385,8 +427,8 @@ weston_device_repick(struct wl_input_device *device, uint32_t time)
 
 	focus = (struct weston_surface *) device->grab->focus;
 	if (focus)
-		weston_surface_transform(focus, device->x, device->y,
-					 &device->grab->x, &device->grab->y);
+		weston_surface_from_global(focus, device->x, device->y,
+					   &device->grab->x, &device->grab->y);
 }
 
 WL_EXPORT void
@@ -536,23 +578,27 @@ texture_region(struct weston_surface *es, pixman_region32_t *region)
 
 static void
 transform_vertex(struct weston_surface *surface,
-		 GLfloat x, GLfloat y, GLfloat u, GLfloat v, GLfloat *r)
+		 GLfloat sx, GLfloat sy,
+		 GLfloat tex_x, GLfloat tex_y, GLfloat *r)
 {
-	struct weston_vector t;
+	/* surface->transform.enabled must always be 1 here. */
 
-	t.f[0] = x;
-	t.f[1] = y;
-	t.f[2] = 0.0;
-	t.f[3] = 1.0;
+	struct weston_vector v = { { sx, sy, 0.0f, 1.0f } };
 
-	weston_matrix_transform(&surface->transform.matrix, &t);
+	v.f[0] += surface->x;
+	v.f[1] += surface->y;
 
-	/* XXX: assumes last row of matrix is [0 0 * 1] */
+	weston_matrix_transform(&surface->transform.matrix, &v);
+
+	if (fabsf(v.f[3]) < 1e-6) {
+		fprintf(stderr, "warning: numerical instability in "
+			"transform_vertex(), divisor = %g\n", v.f[3]);
+	}
 
-	r[ 0] = t.f[0];
-	r[ 1] = t.f[1];
-	r[ 2] = u;
-	r[ 3] = v;
+	r[ 0] = v.f[0] / v.f[3];
+	r[ 1] = v.f[1] / v.f[3];
+	r[ 2] = tex_x;
+	r[ 3] = tex_y;
 }
 
 static int
@@ -565,11 +611,10 @@ texture_transformed_surface(struct weston_surface *es)
 	v = wl_array_add(&ec->vertices, 16 * sizeof *v);
 	p = wl_array_add(&ec->indices, 6 * sizeof *p);
 
-	transform_vertex(es, es->x, es->y, 0.0, 0.0, &v[0]);
-	transform_vertex(es, es->x, es->y + es->height, 0.0, 1.0, &v[4]);
-	transform_vertex(es, es->x + es->width, es->y, 1.0, 0.0, &v[8]);
-	transform_vertex(es, es->x + es->width, es->y + es->height,
-			 1.0, 1.0, &v[12]);
+	transform_vertex(es, 0, 0, 0.0, 0.0, &v[0]);
+	transform_vertex(es, 0, es->height, 0.0, 1.0, &v[4]);
+	transform_vertex(es, es->width, 0, 1.0, 0.0, &v[8]);
+	transform_vertex(es, es->width, es->height, 1.0, 1.0, &v[12]);
 
 	p[0] = 0;
 	p[1] = 1;
@@ -1096,7 +1141,7 @@ weston_compositor_pick_surface(struct weston_compositor *compositor,
 	wl_list_for_each(surface, &compositor->surface_list, link) {
 		if (surface->surface.resource.client == NULL)
 			continue;
-		weston_surface_transform(surface, x, y, sx, sy);
+		weston_surface_from_global(surface, x, y, sx, sy);
 		if (0 <= *sx && *sx < surface->width &&
 		    0 <= *sy && *sy < surface->height)
 			return surface;
@@ -1484,7 +1529,7 @@ notify_touch(struct wl_input_device *device, uint32_t time, int touch_id,
 			touch_set_focus(wd, &es->surface, time);
 		} else if (wd->touch_focus) {
 			es = (struct weston_surface *) wd->touch_focus;
-			weston_surface_transform(es, x, y, &sx, &sy);
+			weston_surface_from_global(es, x, y, &sx, &sy);
 		}
 
 		if (wd->touch_focus_resource && wd->touch_focus)
@@ -1498,7 +1543,7 @@ notify_touch(struct wl_input_device *device, uint32_t time, int touch_id,
 		if (!es)
 			break;
 
-		weston_surface_transform(es, x, y, &sx, &sy);
+		weston_surface_from_global(es, x, y, &sx, &sy);
 		if (wd->touch_focus_resource)
 			wl_resource_post_event(wd->touch_focus_resource,
 					       touch_type, time,
diff --git a/src/compositor.h b/src/compositor.h
index 7555e85..7623921 100644
--- a/src/compositor.h
+++ b/src/compositor.h
@@ -267,6 +267,14 @@ void
 weston_surface_update_transform(struct weston_surface *surface);
 
 void
+weston_surface_to_global(struct weston_surface *surface,
+			 int32_t sx, int32_t sy, int32_t *x, int32_t *y);
+
+void
+weston_surface_from_global(struct weston_surface *surface,
+			   int32_t x, int32_t y, int32_t *sx, int32_t *sy);
+
+void
 weston_device_repick(struct wl_input_device *device, uint32_t time);
 
 void
diff --git a/src/shell.c b/src/shell.c
index d6e0205..d2b2379 100644
--- a/src/shell.c
+++ b/src/shell.c
@@ -1037,7 +1037,6 @@ rotate_binding(struct wl_input_device *device, uint32_t time,
 		(struct weston_surface *) device->pointer_focus;
 	struct shell_surface *surface;
 	struct rotate_grab *rotate;
-	struct weston_vector center = { { 0.0f, 0.0f, 0.0f, 1.0f } };
 
 	if (base_surface == NULL)
 		return;
@@ -1056,21 +1055,17 @@ rotate_binding(struct wl_input_device *device, uint32_t time,
 			break;
 	}
 
-	center.f[0] = 0.5f * surface->surface->width;
-	center.f[1] = 0.5f * surface->surface->height;
-	weston_surface_update_transform(surface->surface);
-	weston_matrix_transform(&surface->surface->transform.matrix, &center);
-	if (fabsf(center.f[3]) < 1e-6)
-		return;
-
 	rotate = malloc(sizeof *rotate);
 	if (!rotate)
 		return;
 
 	rotate->grab.interface = &rotate_grab_interface;
 	rotate->surface = surface;
-	rotate->center.x = center.f[0] / center.f[3];
-	rotate->center.y = center.f[1] / center.f[3];
+
+	weston_surface_to_global(surface->surface,
+				 surface->surface->width / 2,
+				 surface->surface->height / 2,
+				 &rotate->center.x, &rotate->center.y);
 
 	wl_input_device_start_grab(device, &rotate->grab, time);
 	wl_input_device_set_pointer_focus(device, NULL, time, 0, 0, 0, 0);