[pitivi] timeline: Fix title previewer showing text twice

[Alexandru Băluț <alexbalut src gnome org>]

commit 3d1ef8c3966d1ddba4bc44cdc39af1898f7aa99a
Author: Alexandru Băluț <alexandru balut gmail com>
Date:   Mon Dec 6 01:21:31 2021 +0100

    timeline: Fix title previewer showing text twice
    
    The previewer expected the rectangle to be drawn to be the entire
    surface. Since the markers box overlapping the top part, it needs
    to be drawn separately sometimes.
    
    Fixes #2592

 pitivi/timeline/previewers.py | 75 +++++++++++++++++++++++++------------------
 1 file changed, 44 insertions(+), 31 deletions(-)
---
diff --git a/pitivi/timeline/previewers.py b/pitivi/timeline/previewers.py
index 0433407cb..d9c8110af 100644
--- a/pitivi/timeline/previewers.py
+++ b/pitivi/timeline/previewers.py
@@ -1408,7 +1408,15 @@ class TitlePreviewer(Gtk.Layout, Previewer, Zoomable, Loggable):
             self.queue_draw()
 
     def do_draw(self, context):
-        rect = Gdk.cairo_get_clip_rectangle(context)[1]
+        width = self.get_allocated_width()
+        height = self.get_allocated_height()
+
+        # The rect that needs to be drawn
+        exists, rect = Gdk.cairo_get_clip_rectangle(context)
+        if not exists:
+            return
+
+        # Text color white
         context.set_source_rgb(1, 1, 1)
 
         # Get text
@@ -1420,41 +1428,46 @@ class TitlePreviewer(Gtk.Layout, Previewer, Zoomable, Loggable):
 
         # Adapt to RTL/LTR direction
         direction = Pango.unichar_direction(escaped_text[0])
-        if direction in (Pango.Direction.LTR, Pango.Direction.NEUTRAL):
-            stops = (0, 1)
-            x_pos = 10
-            grad = cairo.LinearGradient(rect.width * 0.66, 0,
-                                        rect.width * 0.91, 0)
+        ltr = direction in (Pango.Direction.LTR, Pango.Direction.NEUTRAL)
+
+        x_pos = 10 if ltr else -10
+        y_pos = int((height / 2) - 11)
+        # Draw the text only if it intersects the rectangle to be drawn.
+        if rect.y + rect.height > y_pos:
+            # Setup Pango layout for drawing the text.
+            layout = PangoCairo.create_layout(context)
+            layout.set_markup(escaped_text, -1)
+
+            layout.set_auto_dir(True)
+            layout.set_font_description(self._font_desc)
+            layout.set_width(width * Pango.SCALE)
+
+            # Prevent lines from being wrapped
+            layout.set_ellipsize(Pango.EllipsizeMode.END)
+
+            # Draw text
+            context.move_to(x_pos, y_pos)
+            PangoCairo.show_layout(context, layout)
+
+        # Draw gradient on top of text to make the text "fade out".
+        # The gradient is mostly transparent and turning opaque at the very end.
+        if ltr:
+            x0 = width * 0.66
+            x1 = width * 0.91
         else:
-            stops = (1, 0)
-            x_pos = -10
-            grad = cairo.LinearGradient(rect.width * 0.09, 0,
-                                        rect.width * 0.34, 0)
-
-        # Gradient to make text "fade out"
+            x0 = width * 0.09
+            x1 = width * 0.34
+        # Control vector of the gradient is x0 -> x1.
+        grad = cairo.LinearGradient(x0, 0, x1, 0)
         if self._selected:
             color = (0.14, 0.133, 0.15)
         else:
             color = (0.368, 0.305, 0.4)
-
-        grad.add_color_stop_rgba(stops[0], color[0], color[1], color[2], 0)
-        grad.add_color_stop_rgba(stops[1], color[0], color[1], color[2], 1)
-
-        # Setup Pango layout
-        layout = PangoCairo.create_layout(context)
-        layout.set_auto_dir(True)
-        layout.set_font_description(self._font_desc)
-        layout.set_width(rect.width * Pango.SCALE)
-
-        # Prevent lines from being wrapped
-        layout.set_ellipsize(Pango.EllipsizeMode.END)
-
-        # Draw text
-        layout.set_markup(escaped_text, -1)
-        context.move_to(x_pos, (rect.height / 2) - 11)
-        PangoCairo.show_layout(context, layout)
-
-        # Draw gradient
+        # Set the start offset of the control vector to transparent (if ltr).
+        grad.add_color_stop_rgba(0.0, color[0], color[1], color[2], 0 if ltr else 1)
+        # Set the end offset of the control vector to opaque (if ltr).
+        grad.add_color_stop_rgba(1.0, color[0], color[1], color[2], 1 if ltr else 0)
+        # The rectangle to be filled represents the entire surface.
         context.rectangle(0, 0, rect.width, rect.height)
         context.set_source(grad)
         context.fill()