[pazos]

Originally Posted by NiLuJe

@pazos: The second hunk does make sense, but it's missing getting the width/height from buffer, too, because right now it uses the image buffer but with the framebuffer's dimensions .

(Which I realize may be the point, but then what happens if image buffer's dimension != framebuffer's dimension?)

It seems that I was lucky on my tests. A "cover" that doesn't match framebuffer dimension is attached.

And the proper code, as suggested, would be:

--- a/ffi/blitbuffer.lua
+++ b/ffi/blitbuffer.lua
@@ -1760,17 +1760,19 @@ write blitbuffer contents to a PNG file
 @param filename the name of the file to be created
 --]]
 local Png  -- lazy load ffi/png
-function BB_mt.__index:writePNG(filename, bgr)
+function BB_mt.__index:writePNG(filename, bgr, buffer)
     if not Png then Png = require("ffi/png") end
     local hook, mask, _ = debug.gethook()
     debug.sethook()
-    local w, h = self:getWidth(), self:getHeight()
+    local w = buffer and buffer:getWidth() or self:getWidth()
+    local h = buffer and buffer:getHeight() or self:getHeight()
     local cdata = C.malloc(w * h * 4)
     local mem = ffi.cast("char*", cdata)
     for y = 0, h-1 do
         local offset = 4 * w * y
         for x = 0, w-1 do
-            local c = self:getPixel(x, y):getColorRGB32()
+            local c = buffer and buffer:getPixel(x, y):getColorRGB32() or
+                self:getPixel(x, y):getColorRGB32()
             -- NOTE: Kobo's FB is BGR(A), we already trick MuPDF into doing it that way for us, so, keep faking it here!
             if bgr then
                 mem[offset] = c.b