Merge pull request #774 from Textualize/dont-render-zero-opacity-text

Minimise rendering when text-opacity/opacity is zero

docs/guide/app.md

@@ -84,7 +84,7 @@ Widgets are self-contained components responsible for generating the output for
 
 Widgets can be as simple as a piece of text, a button, or a fully-fledge component like a text editor or file browser (which may contain widgets of their own).
 
-### Composing 
+### Composing
 
 To add widgets to your app implement a [`compose()`][textual.app.App.compose] method which should return a iterable of Widget instances. A list would work, but it is convenient to yield widgets, making the method a *generator*.
 
@@ -107,7 +107,7 @@ While composing is the preferred way of adding widgets when your app starts it i
 
 Here's an app which adds the welcome widget in response to any key press:
 
-```python title="widgets02.py" 
+```python title="widgets02.py"
 --8<-- "docs/examples/app/widgets02.py"
 ```
 
@@ -122,7 +122,7 @@ An app will run until you call [App.exit()][textual.app.App.exit] which will exi
 
 The exit method will also accept an optional positional value to be returned by `run()`. The following example uses this to return the `id` (identifier) of a clicked button.
 
-```python title="question01.py" 
+```python title="question01.py"
 --8<-- "docs/examples/app/question01.py"
 ```
 
@@ -161,7 +161,7 @@ The following example sets the `css_path` attribute on the app:
 
 If the path is relative (as it is above) then it is taken as relative to where the app is defined. Hence this example references `"question01.css"` in the same directory as the Python code. Here is that CSS file:
 
-```sass title="question02.css" 
+```sass title="question02.css"
 --8<-- "docs/examples/app/question02.css"
 ```
 

sandbox/darren/just_a_box.css

@@ -1,8 +1,10 @@
 Screen {
+    layout: center;
     background: darkslategrey;
 }
 
-.box1 {
+#box1 {
     background: darkmagenta;
     width: auto;
+    padding: 4 8;
 }

sandbox/darren/just_a_box.py

@@ -1,12 +1,27 @@
 from __future__ import annotations
 
 from textual.app import App, ComposeResult
-from textual.widgets import Static
+from textual.binding import Binding
+from textual.widgets import Static, Footer
 
 
 class JustABox(App):
+    BINDINGS = [
+        Binding(key="t", action="text_fade_out", description="text-opacity fade out"),
+        Binding(key="o", action="widget_fade_out", description="opacity fade out"),
+    ]
+
     def compose(self) -> ComposeResult:
-        yield Static("Hello, world!", classes="box1")
+        yield Static("Hello, world!", id="box1")
+        yield Footer()
+
+    def action_text_fade_out(self) -> None:
+        box = self.query_one("#box1")
+        self.animator.animate(box.styles, "text_opacity", value=0.0, duration=1)
+
+    def action_widget_fade_out(self) -> None:
+        box = self.query_one("#box1")
+        self.animator.animate(box.styles, "opacity", value=0.0, duration=1)
 
 
 app = JustABox(watch_css=True, css_path="../darren/just_a_box.css")

src/textual/_compositor.py

@@ -604,19 +604,28 @@ class Compositor:
         # up to this point.
         _rich_traceback_guard = True
 
+        def is_visible(widget: Widget) -> bool:
+            """Return True if the widget is (literally) visible by examining various
+            properties which affect whether it can be seen or not."""
+            return (
+                widget.visible
+                and not widget.is_transparent
+                and widget.styles.opacity > 0
+            )
+
         if self.map:
             if crop:
                 overlaps = crop.overlaps
                 mapped_regions = [
                     (widget, region, order, clip)
                     for widget, (region, order, clip, *_) in self.map.items()
-                    if widget.visible and not widget.is_transparent and overlaps(crop)
+                    if is_visible(widget) and overlaps(crop)
                 ]
             else:
                 mapped_regions = [
                     (widget, region, order, clip)
                     for widget, (region, order, clip, *_) in self.map.items()
-                    if widget.visible and not widget.is_transparent
+                    if is_visible(widget)
                 ]
 
             widget_regions = sorted(mapped_regions, key=itemgetter(2), reverse=True)

src/textual/renderables/text_opacity.py

@@ -1,6 +1,7 @@
 import functools
 from typing import Iterable
 
+from rich.cells import cell_len
 from rich.color import Color
 from rich.console import ConsoleOptions, Console, RenderResult, RenderableType
 from rich.segment import Segment
@@ -59,19 +60,25 @@ class TextOpacity:
 
         """
         _Segment = Segment
-        for segment in segments:
-            text, style, control = segment
-            if not style:
-                yield segment
-                continue
+        _from_color = Style.from_color
+        if opacity == 0:
+            for text, style, control in segments:
+                invisible_style = _from_color(bgcolor=style.bgcolor)
+                yield _Segment(cell_len(text) * " ", invisible_style)
+        else:
+            for segment in segments:
+                text, style, control = segment
+                if not style:
+                    yield segment
+                    continue
 
-            color = style.color
-            bgcolor = style.bgcolor
-            if color and color.triplet and bgcolor and bgcolor.triplet:
-                color_style = _get_blended_style_cached(bgcolor, color, opacity)
-                yield _Segment(text, style + color_style)
-            else:
-                yield segment
+                color = style.color
+                bgcolor = style.bgcolor
+                if color and color.triplet and bgcolor and bgcolor.triplet:
+                    color_style = _get_blended_style_cached(bgcolor, color, opacity)
+                    yield _Segment(text, style + color_style)
+                else:
+                    yield segment
 
     def __rich_console__(
         self, console: Console, options: ConsoleOptions

tests/renderables/test_text_opacity.py

@@ -19,10 +19,9 @@ def test_simple_text_opacity(text):
     )
 
 
-def test_value_zero_sets_foreground_color_to_background_color(text):
-    foreground = background = "0;255;0"
+def test_value_zero_doesnt_render_the_text(text):
     assert render(TextOpacity(text, opacity=0)) == (
-        f"\x1b[38;2;{foreground};48;2;{background}mHello, world!{STOP}"
+        f"\x1b[48;2;0;255;0m             {STOP}"
     )