Added support for set_pixel_ratio to offscreen canvas (#122)

Author: almarklein

rendercanvas/base.py

@@ -566,7 +566,13 @@ def is_closed(self):
     # implement the methods they can, but these features are likely not critical.
 
     def set_logical_size(self, width: float, height: float) -> None:
-        """Set the window size (in logical pixels)."""
+        """Set the window size (in logical pixels).
+
+        This changes the physical size of the canvas, such that the new logical
+        size matches the given width and height. Since the physical size is
+        integer (i.e. rounded), the re-calculated logical size may differ slightly
+        from the given width and height (depending on the pixel ratio).
+        """
         width, height = float(width), float(height)
         if width < 0 or height < 0:
             raise ValueError("Canvas width and height must not be negative")

rendercanvas/offscreen.py

@@ -72,6 +72,7 @@ def _rc_present_bitmap(self, *, data, format, **kwargs):
 
     def _rc_set_logical_size(self, width, height):
         logical_size = float(width), float(height)
+
         physical_size = (
             int(logical_size[0] * self._pixel_ratio),
             int(logical_size[1] * self._pixel_ratio),
@@ -94,6 +95,24 @@ def _rc_set_cursor(self, cursor):
 
     # %% Extra API
 
+    def set_physical_size(self, width: int, height: int):
+        """Set the size of the backbuffer (in physical pixels).
+
+        The logical size is re-calculated using the current pixel ratio.
+        """
+        physical_size = int(width), int(height)
+        self._set_size_info(physical_size, self._pixel_ratio)
+
+    def set_pixel_ratio(self, pixel_ratio: float):
+        """Set the pixel ratio, changing the logical size of the canvas.
+
+        The physical size remains the same. If you want to retain a certain
+        logical size, first set the pixel ratio and then the logical size.
+        """
+        self._pixel_ratio = float(pixel_ratio)
+        physical_size = self.get_physical_size()
+        self._set_size_info(physical_size, self._pixel_ratio)
+
     def draw(self):
         """Perform a draw and get the resulting image.