From 50918c652cd4130ad3daa5389e6a0d9a38eb740f Mon Sep 17 00:00:00 2001
From: David Elliott <dfe@tgwbd.org>
Date: Wed, 1 Aug 2007 04:14:12 +0000
Subject: [PATCH] Make masks and alpha work for wxCOPY when blitting a selected
 bitmap from a wxMemoryDC with an eye towards possibly doing more in the
 future.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@47838 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
---
 src/cocoa/dcmemory.mm | 54 +++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 52 insertions(+), 2 deletions(-)

diff --git a/src/cocoa/dcmemory.mm b/src/cocoa/dcmemory.mm
index b6de98c880..9b1a0e9f85 100644
--- a/src/cocoa/dcmemory.mm
+++ b/src/cocoa/dcmemory.mm
@@ -78,6 +78,12 @@ void wxMemoryDC::DoSelect( const wxBitmap& bitmap )
     {
         CocoaTakeFocus();
         wxASSERT(m_cocoaNSImage);
+        // Replace the bitmap's native data with a newly created one based on the
+        // NSImage that has been (potentially) drawn upon.  Note that this may and
+        // probably will in many cases change the bitmap's format.
+        // There is nothing we can do about this using pure Cocoa code.  Even using
+        // CGBitmapContext is not an option because it only supports a limited
+        // number of bitmap formats.  Specifically, 24-bpp is not supported.
         m_selectedBitmap.SetNSBitmapImageRep(
             [[NSBitmapImageRep alloc]
                 initWithFocusedViewRect:NSMakeRect(0.0,0.0,
@@ -96,6 +102,16 @@ void wxMemoryDC::DoSelect( const wxBitmap& bitmap )
                     m_selectedBitmap.GetHeight())];
 
         // Now copy the data
+        // Pass false to GetNSImage so the mask is not applied as an alpha channel.
+        // Cocoa uses premultiplied alpha so applying the mask would cause all
+        // color information masked out to be turned black which is undesirable.
+        // FIXME: Currently, the mask will not be updated if any drawing occurs.
+        // My only suggestion is for wxCocoa users to eschew the mask in favor
+        // of an alpha channel or to recreate the mask after drawing.
+        // The only way to fix this is to draw twice, once as normal and again
+        // onto the mask to update it.  That would require overriding every
+        // single drawing primitive (e.g. DoDrawLine, DoDrawRectangle, etc.)
+        // and would be a major undertaking.
         NSImage *nsimage = [m_selectedBitmap.GetNSImage(false) retain];
         [m_cocoaNSImage lockFocus];
         [nsimage drawAtPoint: NSMakePoint(0,0)
@@ -142,14 +158,48 @@ bool wxMemoryDC::CocoaDoBlitOnFocusedDC(wxCoord xdest, wxCoord ydest,
     [transform concat];
     [flipTransform concat];
 
+    NSImage *sourceImage;
+    if(useMask)
+    {
+        sourceImage = [m_cocoaNSImage copy];
+        // Apply the mask to the copied image
+        NSBitmapImageRep *maskRep = m_selectedBitmap.GetMask()->GetNSBitmapImageRep();
+        NSImage *maskImage = [[NSImage alloc] initWithSize:[maskRep size]];
+        [maskImage addRepresentation:maskRep];
+        [sourceImage lockFocus];
+        [maskImage compositeToPoint:NSZeroPoint operation:NSCompositeDestinationIn];
+        [sourceImage unlockFocus];
+        [maskImage release];
+    }
+    else
+    {   // retain the m_cocoaNSImage so it has the same ownership as the copy done in the other case.
+        sourceImage = [m_cocoaNSImage retain];
+    }
+    NSCompositingOperation drawingOp;
+    switch(logicalFunc)
+    {
+    case wxCOPY:
+        // Even if not using the mask, the image might have an alpha channel
+        // so always use NSCompositeSourceOver.  If the image is fully opaque
+        // it works out the same as NSCompositeCopy.
+        drawingOp = NSCompositeSourceOver;
+        break;
+    // FIXME: implement more raster ops
+    default:
+        wxLogDebug(wxT("wxCocoa does not support blitting with raster operation %d."), logicalFunc);
+        // Just use the default operation.
+        drawingOp = NSCompositeCopy;
+    }
+
     wxLogTrace(wxTRACE_COCOA,wxT("[m_cocoaNSImage isFlipped]=%d"), [m_cocoaNSImage isFlipped]);
-    [m_cocoaNSImage drawAtPoint: NSMakePoint(0,0)
+    [sourceImage drawAtPoint: NSMakePoint(0,0)
         fromRect: NSMakeRect(xsrc,
             m_selectedBitmap.GetHeight()-height-ysrc,
             width, height)
-        operation: NSCompositeCopy // FIXME: raster ops
+        operation: drawingOp
         fraction: 1.0];
 
+    [sourceImage release]; // It was either retained, copied, or allocated.
     [context restoreGraphicsState];
     return false;
 }
-- 
2.45.2