From 7569a2e932bc208000aff5967b87296ca2dd6f5d Mon Sep 17 00:00:00 2001
From: Nicolas Dufresne <nicolas.dufresne@collabora.co.uk>
Date: Thu, 23 Jul 2015 15:19:47 -0400
Subject: [PATCH] basetextoverlay: Fix clipping issues

This patch uses the ink rectangle in order to compute the size
of the surface require to render. It also correctly compute the
transformation matrix as the ink_rect position might not be at
0, 0. Additionally, shadow_offset and outline_offset (which is
in fact the diameter of a dot, not a really an offset) is now
taken into account. Redundant matrix operation has been removed
for the vertical rendering.

Take note that the matrix operation in cairo are excuted in
reverse order.

https://bugzilla.gnome.org/show_bug.cgi?id=728636
---
 ext/pango/gstbasetextoverlay.c | 67 +++++++++++++++++++---------------
 1 file changed, 37 insertions(+), 30 deletions(-)

diff --git a/ext/pango/gstbasetextoverlay.c b/ext/pango/gstbasetextoverlay.c
index ae7b216e86..b649db64fa 100644
--- a/ext/pango/gstbasetextoverlay.c
+++ b/ext/pango/gstbasetextoverlay.c
@@ -1566,9 +1566,12 @@ gst_base_text_overlay_render_pangocairo (GstBaseTextOverlay * overlay,
   cairo_surface_t *surface;
   PangoRectangle ink_rect, logical_rect;
   cairo_matrix_t cairo_matrix;
-  int width, height;
+  gint unscaled_width, unscaled_height;
+  gint width, height;
   double scalef = 1.0;
   double a, r, g, b;
+  gdouble shadow_offset = 0.0;
+  gdouble outline_offset = 0.0;
   GstBuffer *buffer;
   GstMapInfo map;
 
@@ -1579,6 +1582,14 @@ gst_base_text_overlay_render_pangocairo (GstBaseTextOverlay * overlay,
     scalef = (double) (overlay->width) / DEFAULT_SCALE_BASIS;
   }
 
+  if (overlay->draw_shadow)
+    shadow_offset = overlay->shadow_offset;
+
+  /* This value is uses as cairo line width, which is the diameter of a pen
+   * that is circular. That's why only half of it is used to offset */
+  if (overlay->draw_outline)
+    outline_offset = overlay->outline_offset;
+
   pango_layout_set_width (overlay->layout, -1);
   /* set text on pango layout */
   pango_layout_set_markup (overlay->layout, string, textlen);
@@ -1586,7 +1597,8 @@ gst_base_text_overlay_render_pangocairo (GstBaseTextOverlay * overlay,
   /* get subtitle image size */
   pango_layout_get_pixel_extents (overlay->layout, &ink_rect, &logical_rect);
 
-  width = ceil ((logical_rect.width + overlay->shadow_offset) * scalef);
+  unscaled_width = ink_rect.width + shadow_offset + outline_offset;
+  width = ceil (unscaled_width * scalef);
 
   if (width + overlay->deltax >
       (overlay->use_vertical_render ? overlay->height : overlay->width)) {
@@ -1596,11 +1608,13 @@ gst_base_text_overlay_render_pangocairo (GstBaseTextOverlay * overlay,
      */
     gst_base_text_overlay_update_wrap_mode (overlay);
     pango_layout_get_pixel_extents (overlay->layout, &ink_rect, &logical_rect);
+    unscaled_width = ink_rect.width + shadow_offset + outline_offset;
     width = overlay->width;
   }
 
-  height = ceil (
-      (logical_rect.height + logical_rect.y + overlay->shadow_offset) * scalef);
+  unscaled_height = ink_rect.height + shadow_offset + outline_offset;
+  height = ceil (unscaled_height * scalef);
+
   if (height > overlay->height) {
     height = overlay->height;
   }
@@ -1610,40 +1624,33 @@ gst_base_text_overlay_render_pangocairo (GstBaseTextOverlay * overlay,
   height = ceil (height * overlay->render_scale);
   scalef *= overlay->render_scale;
 
+  /* Prepare the transformation matrix. Note that the transformation happens
+   * in reverse order. So for horizontal text, we will translate and then
+   * scale. This is important to understand which scale shall be used. */
+  cairo_matrix_init_scale (&cairo_matrix, scalef, scalef);
+
   if (overlay->use_vertical_render) {
-    PangoRectangle rect;
-    PangoContext *context;
-    PangoMatrix matrix = PANGO_MATRIX_INIT;
-    int tmp;
+    gint tmp;
 
-    context = pango_layout_get_context (overlay->layout);
-
-    pango_matrix_rotate (&matrix, -90);
-
-    rect.x = rect.y = 0;
-    rect.width = width;
-    rect.height = height;
-    pango_matrix_transform_pixel_rectangle (&matrix, &rect);
-    matrix.x0 = -rect.x;
-    matrix.y0 = -rect.y;
-
-    pango_context_set_matrix (context, &matrix);
-
-    cairo_matrix.xx = matrix.xx;
-    cairo_matrix.yx = matrix.yx;
-    cairo_matrix.xy = matrix.xy;
-    cairo_matrix.yy = matrix.yy;
-    cairo_matrix.x0 = matrix.x0;
-    cairo_matrix.y0 = matrix.y0;
-    cairo_matrix_scale (&cairo_matrix, scalef, scalef);
+    /* tranlate to the center of the image, rotate, and tranlate the rotated
+     * image back to the right place */
+    cairo_matrix_translate (&cairo_matrix, unscaled_height / 2.0l,
+        unscaled_width / 2.0l);
+    /* 90 degree clockwise rotation which is PI / 2 in radiants */
+    cairo_matrix_rotate (&cairo_matrix, G_PI_2);
+    cairo_matrix_translate (&cairo_matrix, -(unscaled_width / 2.0l),
+        -(unscaled_height / 2.0l));
 
+    /* Swap width and height */
     tmp = height;
     height = width;
     width = tmp;
-  } else {
-    cairo_matrix_init_scale (&cairo_matrix, scalef, scalef);
   }
 
+  cairo_matrix_translate (&cairo_matrix,
+      ceil (outline_offset / 2.0l) - ink_rect.x,
+      ceil (outline_offset / 2.0l) - ink_rect.y);
+
   /* reallocate overlay buffer */
   buffer = gst_buffer_new_and_alloc (4 * width * height);
   gst_buffer_replace (&overlay->text_image, buffer);