[Scummvm-git-logs] scummvm master -> 40fc49256dc766d98789f57ee967bc94b7e46c8a

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Summary:
40fc49256d SLUDGE: Make sure initial backdrop gets its alpha channel stored


Commit: 40fc49256dc766d98789f57ee967bc94b7e46c8a
    https://github.com/scummvm/scummvm/commit/40fc49256dc766d98789f57ee967bc94b7e46c8a
Author: Sebastian Krzyszkowiak (dos at dosowisko.net)
Date: 2023-01-16T17:57:04+01:00

Commit Message:
SLUDGE: Make sure initial backdrop gets its alpha channel stored

OpenSLUDGE draws the first backdrop image with alpha channel
intact. Afterwards, next images are blended with previous backdrop
contents.

So far ScummVM always did the later part, but never the former,
which caused parallax to not work as it relies on alpha channel
being propagated into backdrop (which gets initiallly filled
with opaque black, so it had no chance to ever be transparent).

Fix that by clearing the area the first backdrop image is about
to get blitted into with full transparency.

Changed paths:
    engines/sludge/backdrop.cpp


diff --git a/engines/sludge/backdrop.cpp b/engines/sludge/backdrop.cpp
index 0479bc6f0c4..a6710d7496f 100644
--- a/engines/sludge/backdrop.cpp
+++ b/engines/sludge/backdrop.cpp
@@ -430,6 +430,9 @@ bool GraphicsManager::loadHSI(int num, Common::SeekableReadStream *stream, int x
 		return false;
 	}
 
+	if (!_backdropExists)
+		_backdropSurface.fillRect(Common::Rect(x, y, x + tmp.w, y + tmp.h), _renderSurface.format.ARGBToColor(0, 0, 0, 0));
+
 	// copy surface loaded to backdrop
 	Graphics::TransparentSurface tmp_trans(tmp, false);
 	tmp_trans.blit(_backdropSurface, x, y);