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Fix BMP palette loading #386

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Merged
merged 5 commits into from
Jan 25, 2025
Merged

Fix BMP palette loading #386

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3132dfb
Core (LV::Video): Fix BMP loader not returning error despite not supp…
kaixiong Jan 23, 2025
17dcf87
Core (LV::Video): Fix BMP loader not loading palette from the correct…
kaixiong Jan 23, 2025
0b41ed7
Core (LV::Video): Check palettes are equal in has_same_content().
kaixiong Jan 23, 2025
54a9d7e
Core (LV::Video): Add BI_BITFIELDS #define in BMP loader for clarity.
kaixiong Jan 25, 2025
175e9b2
Core (LV::Video): Additional comments in BMP loader on color table re…
kaixiong Jan 25, 2025
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4 changes: 4 additions & 0 deletions libvisual/libvisual/lv_video.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -392,6 +392,10 @@ namespace LV {
}
}

// Videos must have the same palette.
if (m_impl->palette != video->m_impl->palette)
return false;

return true;
}

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6 changes: 5 additions & 1 deletion libvisual/libvisual/private/lv_video_bmp.cpp
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Expand Up @@ -286,6 +286,8 @@ namespace LV {
fp.read (reinterpret_cast<char*> (&bf_bits), 4);
bf_bits = VISUAL_ENDIAN_LEI32 (bf_bits);

auto dib_header_pos = fp.tellg ();

/* Read the info structure size */
fp.read (reinterpret_cast<char*> (&bi_size), 4);
bi_size = VISUAL_ENDIAN_LEI32 (bi_size);
Expand Down Expand Up @@ -341,12 +343,14 @@ namespace LV {
return nullptr;
}

if (bi_compression > 3) {
if (bi_compression >= 3) {
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@hartwork hartwork Jan 25, 2025

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I'm not a big fan of approach "undocumented unnamed magic number". This seems to be 3 because BI_BITFIELDS == 3 in Windows. If we cannot use that constant without including Windows headers, let's either (a) add a good comment or (b) make our own copy of that constant (or both)?

visual_log (VISUAL_LOG_ERROR, "Bitmap uses an invalid or unsupported compression scheme");
fp.seekg (saved_stream_pos);
return nullptr;
}

fp.seekg (dib_header_pos + std::streampos {bi_size}, std::ios::beg);
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@hartwork hartwork Jan 25, 2025 •
edited
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Let's add comments (or make otherwise more obvious) that…

  • that we're jumping to the start of the palette here (— we could also move the line_below_ comment /* Load the palette */ to better show it's part of palette loading?)
  • that this is the correct value (only) because we ruled out both BI_BITFIELDS and BI_ALPHABITFIELDS earlier (referring to the first paragraph at https://en.wikipedia.org/wiki/BMP_file_format#Color_table)

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@kaixiong kaixiong Jan 25, 2025

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Good idea, let me make that change.


/* Load the palette */
if (bi_bitcount < 24) {
if (bi_clrused == 0) {
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