From 3d40a28a232a52fef44694d30b9432b7bd12134d Mon Sep 17 00:00:00 2001
From: Ivan Mogilko <ikm_spb@yahoo.com>
Date: Sun, 5 Jan 2025 21:23:29 +0300
Subject: [PATCH] Common: fix loaded images without alpha converted to 32-bit

---
 Common/gfx/bitmap.cpp     | 7 +++++--
 Common/gfx/bitmapdata.h   | 7 +++++--
 Common/gfx/image_file.cpp | 9 ++++++++-
 3 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/Common/gfx/bitmap.cpp b/Common/gfx/bitmap.cpp
index ee9ca5b7c17..ae3c4846809 100644
--- a/Common/gfx/bitmap.cpp
+++ b/Common/gfx/bitmap.cpp
@@ -284,7 +284,7 @@ void ReadPixelsFromMemory(Bitmap *dst, const uint8_t *src_buffer, const size_t s
 
 // Converts loaded bitmap to the requested color depth,
 // optionally fixups color palette
-static Bitmap *BitmapColorDepthFixup(Bitmap *bmp, int dst_color_depth, RGB *pal)
+static Bitmap *BitmapColorDepthFixup(Bitmap *bmp, int dst_color_depth, RGB *pal, bool src_has_alpha)
 {
     int bmp_depth = bmp->GetColorDepth();
     int dest_depth = get_color_load_depth(bmp_depth, false);
@@ -301,6 +301,9 @@ static Bitmap *BitmapColorDepthFixup(Bitmap *bmp, int dst_color_depth, RGB *pal)
             bmp->WrapAllegroBitmap(al_bmp, false);
     }
 
+    if ((dest_depth == 32) && !src_has_alpha)
+        BitmapHelper::MakeOpaqueSkipMask(bmp);
+
     /* construct a fake palette if 8-bit mode is not involved */
     if ((bmp_depth != 8) && (dest_depth != 8) && pal)
         generate_332_palette(pal);
@@ -322,7 +325,7 @@ Bitmap* LoadBitmap(Stream *in, const String& ext, int dst_color_depth, RGB *pal)
     if (!bmp)
         return nullptr;
     // Perform color depth and palette fixups
-    Bitmap *fixed_bmp = BitmapColorDepthFixup(bmp, dst_color_depth, pal);
+    Bitmap *fixed_bmp = BitmapColorDepthFixup(bmp, dst_color_depth, pal, pxbuf.HasAlphaChannel());
     if (fixed_bmp != bmp)
         delete bmp;
     return fixed_bmp;
diff --git a/Common/gfx/bitmapdata.h b/Common/gfx/bitmapdata.h
index 3e431be376a..09b48bba3e3 100644
--- a/Common/gfx/bitmapdata.h
+++ b/Common/gfx/bitmapdata.h
@@ -41,6 +41,7 @@ enum PixelFormat
     kPxFmt_R5G6B5,      // 16-bit R5G6B5, historical 16-bit pixel format in AGS
     kPxFmt_R8G8B8,      // 24-bit RGB (no alpha)
     kPxFmt_A8R8G8B8,    // 32-bit ARGB
+    kPxFmt_X8R8G8B8,    // 32-bit RGB with no valid alpha
 };
 
 // Returns bits-per-pixel from format
@@ -55,6 +56,7 @@ inline int PixelFormatToPixelBits(PixelFormat fmt)
     case kPxFmt_R5G6B5:     return 16;
     case kPxFmt_R8G8B8:     return 24;
     case kPxFmt_A8R8G8B8:   return 32;
+    case kPxFmt_X8R8G8B8:   return 32;
     default:                return 0;
     }
 }
@@ -64,7 +66,7 @@ inline int PixelFormatToPixelBytes(PixelFormat fmt)
     return (PixelFormatToPixelBits(fmt) + 7) / 8;
 }
 
-inline PixelFormat ColorDepthToPixelFormat(int color_depth)
+inline PixelFormat ColorDepthToPixelFormat(int color_depth, bool alpha_valid = true)
 {
     switch (color_depth)
     {
@@ -74,7 +76,7 @@ inline PixelFormat ColorDepthToPixelFormat(int color_depth)
     case 15: return kPxFmt_R5G5B5;
     case 16: return kPxFmt_R5G6B5;
     case 24: return kPxFmt_R8G8B8;
-    case 32: return kPxFmt_A8R8G8B8;
+    case 32: return alpha_valid ? kPxFmt_A8R8G8B8 : kPxFmt_X8R8G8B8;
     default: return kPxFmt_Undefined;
     }
 }
@@ -119,6 +121,7 @@ class BitmapData
     operator bool() const { return _cbuf != nullptr; }
 
     inline PixelFormat GetFormat() const { return _format; }
+    inline bool HasAlphaChannel() const { return _format == kPxFmt_A8R8G8B8; }
     inline int GetColorDepth() const { return _bitsPerPixel; }
     inline int GetWidth() const { return _width; }
     inline int GetHeight() const { return _height; }
diff --git a/Common/gfx/image_file.cpp b/Common/gfx/image_file.cpp
index 8b958c5adb0..67ef3975d1d 100644
--- a/Common/gfx/image_file.cpp
+++ b/Common/gfx/image_file.cpp
@@ -559,6 +559,7 @@ PixelBuffer LoadBMP(Stream *in, RGB *pal) {
     int rMask = 0;
     int gMask = 0;
     int bMask = 0;
+    bool hasAlpha = false;
 
     const soff_t format_at = in->GetPosition(); // starting offset
 
@@ -610,6 +611,8 @@ PixelBuffer LoadBMP(Stream *in, RGB *pal) {
             rMask = in->ReadInt32();
             gMask = in->ReadInt32();
             bMask = in->ReadInt32();
+            // TODO: might need to support alpha bits, if it's present in the header
+            // also set hasAlpha = true in such case
         } else {
             bmp_read_palette(hdr.offsetBits - 54, pal, in, false);
         }
@@ -643,7 +646,11 @@ PixelBuffer LoadBMP(Stream *in, RGB *pal) {
     if (bpp < 8)
         bpp = 8;
 
-    PixelBuffer pxdata(w, h, ColorDepthToPixelFormat(bpp));
+    // TODO: if we support loading 32-bit ARGB images (existing old BMP loader code doesn't),
+    // then we might also have to test if there's ANY alpha present in the image
+    // AFTER decoding the pixel data, and adjust the format info (?).
+
+    PixelBuffer pxdata(w, h, ColorDepthToPixelFormat(bpp, hasAlpha));
     if (!pxdata) {
         return {};
     }