LibGfx: Give Bitmap a scale factor

Gfx::Bitmap can now store its scale factor. Normally it's 1, but
in high dpi mode it can be 2.

If a Bitmap with a scale factor of 2 is blitted to a Painter with
scale factor of 2, the pixels can be copied over without any resampling.
(When blitting a Bitmap with a scale factor of 1 to a Painter with scale
factor of 2, the Bitmap is painted at twice its width and height at
paint time. Blitting a Bitmap with a scale factor of 2 to a Painter with
scale factor 1 is not supported.)

A Bitmap with scale factor of 2 reports the same width() and height() as
one with scale factor 1. That's important because many places in the
codebase use a bitmap's width() and height() to layout Widgets, and all
widget coordinates are in logical coordinates as well, per
Documentation/HighDPI.md.

Bitmap grows physical_width() / physical_height() to access the actual
pixel size. Update a few callers that work with pixels to call this
instead.

Make Painter's constructor take its scale factor from the target bitmap
that's passed in, and update its various blit() methods to handle
blitting a 2x bitmap to a 2x painter. This allows removing some gnarly
code in Compositor. (In return, put some new gnarly code in
LibGfxScaleDemo to preserve behavior there.)

No intended behavior change.

1 files changed, 5 insertions, 1 deletions

diff --git a/Userland/Libraries/LibGfx/ShareableBitmap.cpp b/Userland/Libraries/LibGfx/ShareableBitmap.cpp
index c59a2d0dad..9babcd7ea2 100644
--- a/Userland/Libraries/LibGfx/ShareableBitmap.cpp
+++ b/Userland/Libraries/LibGfx/ShareableBitmap.cpp
@@ -55,6 +55,7 @@ bool encode(Encoder& encoder, const Gfx::ShareableBitmap& shareable_bitmap)
     auto& bitmap = *shareable_bitmap.bitmap();
     encoder << IPC::File(bitmap.anon_fd());
     encoder << bitmap.size();
+    encoder << bitmap.scale();
     encoder << (u32)bitmap.format();
     if (bitmap.is_indexed()) {
         auto palette = bitmap.palette_to_vector();
@@ -78,6 +79,9 @@ bool decode(Decoder& decoder, Gfx::ShareableBitmap& shareable_bitmap)
     Gfx::IntSize size;
     if (!decoder.decode(size))
         return false;
+    u32 scale;
+    if (!decoder.decode(scale))
+        return false;
     u32 raw_bitmap_format;
     if (!decoder.decode(raw_bitmap_format))
         return false;
@@ -89,7 +93,7 @@ bool decode(Decoder& decoder, Gfx::ShareableBitmap& shareable_bitmap)
         if (!decoder.decode(palette))
             return false;
     }
-    auto bitmap = Gfx::Bitmap::create_with_anon_fd(bitmap_format, anon_file.take_fd(), size, palette, Gfx::Bitmap::ShouldCloseAnonymousFile::Yes);
+    auto bitmap = Gfx::Bitmap::create_with_anon_fd(bitmap_format, anon_file.take_fd(), size, scale, palette, Gfx::Bitmap::ShouldCloseAnonymousFile::Yes);
     if (!bitmap)
         return false;
     shareable_bitmap = Gfx::ShareableBitmap { bitmap.release_nonnull(), Gfx::ShareableBitmap::ConstructWithKnownGoodBitmap };