Close #12 by using transparent background for PNG export.

README.md

@@ -54,6 +54,8 @@ to put the blocks together. Here are a few ideas for how to make the blocks:
    the blocks bump gently against each other.
 
 Whatever technique you use, glue sticks are easier to work with than white glue.
+If you don't want to print it out, you can also download the image and move the
+pieces around in a paint program.
 
 ## Constructing Your Own
 To construct your own puzzle, you have to construct the crossword puzzle, split

docs/index.md

@@ -57,6 +57,8 @@ to put the blocks together. Here are a few ideas for how to make the blocks:
    the blocks bump gently against each other.
 
 Whatever technique you use, glue sticks are easier to work with than white glue.
+If you don't want to print it out, you can also download the image and move the
+pieces around in a paint program.
 
 ## Constructing Your Own
 To construct your own puzzle, you have to construct the crossword puzzle, split

four_letter_blocks/__main__.py

@@ -238,8 +238,8 @@ def export_png(self, file_path: Path):
         puzzle = self.parse_puzzle()
         width, height = 640, 2000
         pixmap = QPixmap(width, height)
-        white = QColor('white')
-        pixmap.fill(white)
+        transparent = QColor(255, 255, 255, 0)
+        pixmap.fill(transparent)
         painter = QPainter(pixmap)
         height = puzzle.draw_blocks(painter)
         painter.end()

four_letter_blocks/square.py

@@ -1,5 +1,5 @@
 from PySide6.QtCore import QRect, Qt
-from PySide6.QtGui import QPainter
+from PySide6.QtGui import QPainter, QColor, QBrush
 
 
 class Square:
@@ -28,6 +28,8 @@ def draw(self, painter: QPainter):
                      self.y,
                      self.size,
                      self.size)
+        white = QColor('white')
+        painter.setBrush(QBrush(white))
         painter.drawRect(rect)
         font = painter.font()
         number_shift = round(self.size / 20)