Render with external buffer and remove BitmapDataHolder

This is a lot better (and shorter).
Also it's more official PDFium API use, as FPDFBitmap_CreateEx() wasn't
meant to get a stride value if the buffer parameter is None.

docs/devel/changelog_staging.md

@@ -7,5 +7,6 @@
 
 - Rewrote the project's `README.md`. Added more support model examples and an extensive guide regarding the raw PDFium/ctypes API.
 - Improved support model code style while writing the raw API guide.
+- pypdfium2 now provides PDFium with an external buffer for rendering. This has numerous advantages, most notably that callers don't need to free resources anymore. The `BitmapDataHolder` class has been removed. The `render_base()` API was semi-public, so technically this is an API-breaking change.
 - PDFium's commit log is now shown with GitHub releases.
 - Tweaked dependency pinning.

src/pypdfium2/_helpers/page.py

@@ -295,8 +295,8 @@ def render_base(
                 A list of item types that shall not be smoothed (text, image, path).
         
         Returns:
-            (BitmapDataHolder, str, (int, int)):
-            Bitmap data holder, colour format, and image size.
+            (ctypes.c_ubyte_Array_N, str, (int, int)):
+            Ctypes array, colour format, and image size.
             The colour format can be ``BGRA``, ``BGR``, or ``L``, depending on the parameters *colour* and *greyscale*.
             Image size is given in pixels as a tuple of width and height.
         """
@@ -323,7 +323,8 @@ def render_base(
         if any(d < 1 for d in (width, height)):
             raise ValueError("Crop exceeds page dimensions (in px): width %s, height %s, crop %s" % (src_width, src_height, crop))
 
-        bitmap = pdfium.FPDFBitmap_CreateEx(width, height, cl_pdfium, None, width*n_colours)
+        buffer = (ctypes.c_ubyte * (width*height*n_colours))()
+        bitmap = pdfium.FPDFBitmap_CreateEx(width, height, cl_pdfium, buffer, width*n_colours)
         if fpdf_colour is not None:
             pdfium.FPDFBitmap_FillRect(bitmap, 0, 0, width, height, fpdf_colour)
 
@@ -353,14 +354,12 @@ def render_base(
         render_args = (bitmap, self._page, -crop[0], -crop[3], src_width, src_height, RotationToConst[rotation], render_flags)
         pdfium.FPDF_RenderPageBitmap(*render_args)
         pdfium.FPDF_FFLDraw(form_fill, *render_args)
-
-        cbuf_ptr = pdfium.FPDFBitmap_GetBuffer(bitmap)
-        cbuf_array_ptr = ctypes.cast(cbuf_ptr, ctypes.POINTER(ctypes.c_ubyte * (width*height*n_colours)))
-        data_holder = BitmapDataHolder(bitmap, cbuf_array_ptr)
-
         pdfium.FPDFDOC_ExitFormFillEnvironment(form_fill)
 
-        return data_holder, cl_format, (width, height)
+        # No need to call FPDFBitmap_Destroy() because we're using an external buffer.
+        # Python will take care of freeing the memory when `buffer` isn't referenced anymore.
+
+        return buffer, cl_format, (width, height)
 
 
     def render_tobytes(self, *args, **kwargs):
@@ -370,12 +369,8 @@ def render_tobytes(self, *args, **kwargs):
         Returns:
             (bytes, str, (int, int)): Image data, colour format, and size.
         """
-
-        data_holder, cl_format, size = self.render_base(*args, **kwargs)
-        data = bytes( data_holder.get_data() )
-        data_holder.close()
-
-        return data, cl_format, size
+        c_array, cl_format, size = self.render_base(*args, **kwargs)
+        return bytes(c_array), cl_format, size
 
 
     def render_topil(self, *args, **kwargs):
@@ -391,26 +386,12 @@ def render_topil(self, *args, **kwargs):
         if not have_pil:
             raise RuntimeError("Pillow library needs to be installed for render_topil().")
 
-        data_holder, cl_format, size = self.render_base(*args, **kwargs)
-        pil_image = PIL.Image.frombytes(ColourMapping[cl_format], size, data_holder.get_data(), "raw", cl_format, 0, 1)
-        data_holder.close()
+        c_array, cl_format, size = self.render_base(*args, **kwargs)
+        pil_image = PIL.Image.frombytes(ColourMapping[cl_format], size, c_array, "raw", cl_format, 0, 1)
 
         return pil_image
 
 
-class BitmapDataHolder:
-
-    def __init__(self, bm_handle, bm_array_ptr):
-        self.bm_handle = bm_handle
-        self.bm_array_ptr = bm_array_ptr
-
-    def get_data(self):
-        return self.bm_array_ptr.contents
-
-    def close(self):
-        pdfium.FPDFBitmap_Destroy(self.bm_handle)
-
-
 class PdfPageObject:
     """ Page object helper class. """