Fix dpi issue for bitmaps on the OS X backend

dmcdougall · mdboom · commit 9ffe6ca873d2 · 2012-09-18T08:34:31.000-04:00
Bitmaps were being generated from the NSView. NSImages, by default,
always use a dpi of 72. To generate a bitmap of a different size,
the image must be redrawn into a new rect. To resample the image at
a different resolution, a conversion is made to use the new dpi.
diff --git a/lib/matplotlib/backends/backend_macosx.py b/lib/matplotlib/backends/backend_macosx.py
@@ -316,7 +316,7 @@ def _print_bitmap(self, filename, *args, **kwargs):
         width, height = self.figure.get_size_inches()
         width, height = width*dpi, height*dpi
         filename = unicode(filename)
-        self.write_bitmap(filename, width, height)
+        self.write_bitmap(filename, width, height, dpi)
         self.figure.dpi = old_dpi
 
     def print_bmp(self, filename, *args, **kwargs):
diff --git a/src/_macosx.m b/src/_macosx.m
@@ -3509,16 +3509,16 @@ static void _data_provider_release(void* info, const void* data, size_t size)
     int n;
     const unichar* characters;
     NSSize size;
-    double width, height;
+    double width, height, dpi;
 
     if(!view)
     {
         PyErr_SetString(PyExc_RuntimeError, "NSView* is NULL");
         return NULL;
     }
     /* NSSize contains CGFloat; cannot use size directly */
-    if(!PyArg_ParseTuple(args, "u#dd",
-                                &characters, &n, &width, &height)) return NULL;
+    if(!PyArg_ParseTuple(args, "u#ddd",
+                                &characters, &n, &width, &height, &dpi)) return NULL;
     size.width = width;
     size.height = height;
 
@@ -3543,16 +3543,24 @@ static void _data_provider_release(void* info, const void* data, size_t size)
     if (invalid) [view setNeedsDisplay: YES];
 
     NSImage* image = [[NSImage alloc] initWithData: data];
-    [image setScalesWhenResized: YES];
-    [image setSize: size];
-    data = [image TIFFRepresentation];
-    [image release];
+    NSImage *resizedImage = [[NSImage alloc] initWithSize:size];
+
+    [resizedImage lockFocus];
+    [image drawInRect:NSMakeRect(0, 0, width, height) fromRect:NSZeroRect operation:NSCompositeSourceOver fraction:1.0];
+    [resizedImage unlockFocus];
+    data = [resizedImage TIFFRepresentation];
+
+    NSBitmapImageRep* rep = [NSBitmapImageRep imageRepWithData:data];
+
+    NSSize pxlSize = NSMakeSize(rep.pixelsWide, rep.pixelsHigh);
+    NSSize newSize = NSMakeSize(72.0 * pxlSize.width / dpi, 72.0 * pxlSize.height / dpi);
+
+    [rep setSize:newSize];
 
     if (! [extension isEqualToString: @"tiff"] &&
         ! [extension isEqualToString: @"tif"])
     {
         NSBitmapImageFileType filetype;
-        NSBitmapImageRep* bitmapRep = [NSBitmapImageRep imageRepWithData: data];
         if ([extension isEqualToString: @"bmp"])
             filetype = NSBMPFileType;
         else if ([extension isEqualToString: @"gif"])
@@ -3567,9 +3575,10 @@ static void _data_provider_release(void* info, const void* data, size_t size)
             return NULL;
         }
 
-        data = [bitmapRep representationUsingType:filetype properties:nil];
+        data = [rep representationUsingType:filetype properties:nil];
     }
 
+    data = [rep representationUsingType:NSTIFFFileType properties:nil];
     [data writeToFile: filename atomically: YES];
     [pool release];
 
