1 files changed, 128 insertions, 0 deletions
diff --git a/examples/gtk/cairo-knockout.py b/examples/gtk/cairo-knockout.py
new file mode 100755
index 0000000..e8c2c90
--- /dev/null
+++ b/examples/gtk/cairo-knockout.py
@@ -0,0 +1,128 @@
+#!/usr/bin/env python
+"""Based on gtk+/test/testcairo.c
+"""
+
+from __future__ import division
+import math
+import sys
+
+import cairo
+import gtk
+
+
+def oval_path(ctx, xc, yc, xr, yr):
+    ctx.save()
+
+    ctx.translate (xc, yc)
+    ctx.scale (1.0, yr / xr)
+    ctx.move_to (xr, 0.0)
+    ctx.arc (0, 0, xr, 0, 2 * math.pi)
+    ctx.close_path ()
+
+    ctx.restore()
+
+def fill_checks(ctx, x, y, width, height):
+    CHECK_SIZE = 32
+
+    ctx.rectangle (x, y, width, height)
+    ctx.set_source_rgb (0.4, 0.4, 0.4)
+    ctx.fill ()
+
+    # Only works for CHECK_SIZE a power of 2
+    for j in range (x & -CHECK_SIZE, height, CHECK_SIZE):
+        for i in range (y & -CHECK_SIZE, width, CHECK_SIZE):
+            if ((i / CHECK_SIZE + j / CHECK_SIZE) % 2 == 0):
+                ctx.rectangle (i, j, CHECK_SIZE, CHECK_SIZE)
+
+    ctx.set_source_rgb (0.7, 0.7, 0.7)
+    ctx.fill ()
+
+def draw_3circles(ctx, xc, yc, radius, alpha):
+    subradius = radius * (2 / 3. - 0.1)
+
+    ctx.set_source_rgba(1, 0, 0, alpha)
+    oval_path(ctx,
+              xc + radius / 3. * math.cos(math.pi * 0.5),
+              yc - radius / 3. * math.sin(math.pi * 0.5),
+              subradius, subradius)
+    ctx.fill()
+
+    ctx.set_source_rgba(0, 1, 0, alpha)
+    oval_path(ctx,
+              xc + radius / 3. * math.cos(math.pi * (0.5 + 2/.3)),
+              yc - radius / 3. * math.sin(math.pi * (0.5 + 2/.3)),
+              subradius, subradius)
+    ctx.fill()
+
+    ctx.set_source_rgba(0, 0, 1, alpha)
+    oval_path(ctx,
+              xc + radius / 3. * math.cos(math.pi * (0.5 + 4/.3)),
+              yc - radius / 3. * math.sin(math.pi * (0.5 + 4/.3)),
+              subradius, subradius)
+    ctx.fill()
+
+def draw (ctx, width, height):
+    radius = 0.5 * min(width, height) - 10
+    xc = width / 2.
+    yc = height / 2.
+
+    target  = ctx.get_target()
+    overlay = target.create_similar(cairo.CONTENT_COLOR_ALPHA, width, height)
+    punch   = target.create_similar(cairo.CONTENT_ALPHA, width, height)
+    circles = target.create_similar(cairo.CONTENT_COLOR_ALPHA, width, height)
+
+    fill_checks(ctx, 0, 0, width, height)
+
+    # Draw a black circle on the overlay
+    overlay_cr = cairo.Context (overlay)
+    overlay_cr.set_source_rgb (0, 0, 0)
+    oval_path (overlay_cr, xc, yc, radius, radius)
+    overlay_cr.fill()
+
+    # Draw 3 circles to the punch surface, then cut
+    # that out of the main circle in the overlay
+    punch_cr = cairo.Context (punch)
+    draw_3circles (punch_cr, xc, yc, radius, 1.0)
+
+    overlay_cr.set_operator (cairo.OPERATOR_DEST_OUT)
+    overlay_cr.set_source_surface (punch, 0, 0)
+    overlay_cr.paint()
+
+    # Now draw the 3 circles in a subgroup again
+    # at half intensity, and use OperatorAdd to join up
+    # without seams.
+    circles_cr = cairo.Context (circles)
+
+    circles_cr.set_operator (cairo.OPERATOR_OVER)
+    draw_3circles (circles_cr, xc, yc, radius, 0.5)
+
+    overlay_cr.set_operator (cairo.OPERATOR_ADD)
+    overlay_cr.set_source_surface (circles, 0, 0)
+    overlay_cr.paint()
+
+    ctx.set_source_surface (overlay, 0, 0)
+    ctx.paint()
+
+def expose(drawingarea, event):
+    ctx = drawingarea.window.cairo_create()
+
+    _, _, width, height = drawingarea.allocation
+    draw (ctx, width, height)
+
+    return False
+
+def main():
+    win = gtk.Window()
+    win.connect('destroy', gtk.main_quit)
+    win.set_title('Knockout Groups')
+    win.set_default_size(400, 400)
+
+    drawingarea = gtk.DrawingArea()
+    win.add(drawingarea)
+    drawingarea.connect('expose_event', expose)
+
+    win.show_all()
+    gtk.main()
+
+if __name__ == '__main__':
+    main()