Fix squish RGTC_R decompression corruption

[BlueCube3310]

The custom Godot code for squish only allows for decompressing BC5 (RGTC_RG) textures. This means attempting to decompress BC4-compressed images (for the minature texture views, for example) would result in corrupted images:

master	PR

An MRP for testing the changes: RGTCSquishError.zip
Steps to reproduce:

1. Load the project and open Main.tscn
2. Select the mesh instance and look at the Albedo texture preview in the material inspector.

[clayjohn]

Oh wow, doing this was brought up 6 years ago... #13025 (comment)

[clayjohn]

Looks good to me. Tested locally and it works.

One thing to note is that the generated preview for the file system doesn't update (even after deleting the .godot folder). So some users may be surprised to see the corruption in the file system preview

[akien-mga]

One thing to note is that the generated preview for the file system doesn't update (even after deleting the .godot folder). So some users may be surprised to see the corruption in the file system preview

File thumbnails are stored outside the project, in the user cache folder. On Linux it's in ~/.cache/godot/.

[akien-mga]

Could you add your changes to the existing thirdparty/squish/godot-changes.patch so that it fully documents the changes made for Godot?

This should do the trick (also included a minor comment style change for consistency):

diff --git a/thirdparty/squish/colourblock.cpp b/thirdparty/squish/colourblock.cpp
index 49401358bc..f14c9362bd 100644
--- a/thirdparty/squish/colourblock.cpp
+++ b/thirdparty/squish/colourblock.cpp
@@ -24,9 +24,9 @@
    -------------------------------------------------------------------------- */
 
 #include "colourblock.h"
-// -- Godot start --
+// -- GODOT start --
 #include "alpha.h"
-// -- Godot end --
+// -- GODOT end --
 
 namespace squish {
 
diff --git a/thirdparty/squish/godot-changes.patch b/thirdparty/squish/godot-changes.patch
index ef7bafb4b4..655a8cffc2 100644
--- a/thirdparty/squish/godot-changes.patch
+++ b/thirdparty/squish/godot-changes.patch
@@ -1,22 +1,33 @@
 diff --git a/thirdparty/squish/colourblock.cpp b/thirdparty/squish/colourblock.cpp
-index af8b98036..3d87adaa7 100644
+index af8b980365..f14c9362bd 100644
 --- a/thirdparty/squish/colourblock.cpp
 +++ b/thirdparty/squish/colourblock.cpp
 @@ -24,6 +24,9 @@
     -------------------------------------------------------------------------- */
  
  #include "colourblock.h"
-+// -- Godot start --
++// -- GODOT start --
 +#include "alpha.h"
-+// -- Godot end --
++// -- GODOT end --
  
  namespace squish {
  
-@@ -211,4 +214,23 @@ void DecompressColour( u8* rgba, void const* block, bool isDxt1 )
+@@ -211,4 +214,34 @@ void DecompressColour( u8* rgba, void const* block, bool isDxt1 )
      }
  }
  
-+// -- Godot start --
++// -- GODOT start --
++void DecompressColourBc4( u8* rgba, void const* block)
++{
++    DecompressAlphaDxt5(rgba,block);
++    for ( int i = 0; i < 16; ++i ) {
++        rgba[i*4] = rgba[i*4 + 3];
++		rgba[i*4 + 1] = 0;
++		rgba[i*4 + 2] = 0;
++        rgba[i*4 + 3] = 255;
++    }
++}
++
 +void DecompressColourBc5( u8* rgba, void const* block)
 +{
 +    void const* rblock = block;
@@ -37,21 +48,22 @@ index af8b98036..3d87adaa7 100644
 +
  } // namespace squish
 diff --git a/thirdparty/squish/colourblock.h b/thirdparty/squish/colourblock.h
-index fee2cd7c5..3cb9b7e3b 100644
+index fee2cd7c5d..e1eb9e4917 100644
 --- a/thirdparty/squish/colourblock.h
 +++ b/thirdparty/squish/colourblock.h
-@@ -35,6 +35,9 @@ void WriteColourBlock3( Vec3::Arg start, Vec3::Arg end, u8 const* indices, void*
+@@ -35,6 +35,10 @@ void WriteColourBlock3( Vec3::Arg start, Vec3::Arg end, u8 const* indices, void*
  void WriteColourBlock4( Vec3::Arg start, Vec3::Arg end, u8 const* indices, void* block );
  
  void DecompressColour( u8* rgba, void const* block, bool isDxt1 );
 +// -- GODOT start --
++void DecompressColourBc4( u8* rgba, void const* block );
 +void DecompressColourBc5( u8* rgba, void const* block );
 +// -- GODOT end --
  
  } // namespace squish
  
 diff --git a/thirdparty/squish/config.h b/thirdparty/squish/config.h
-index 92edefe96..05f8d7259 100644
+index 92edefe966..05f8d72598 100644
 --- a/thirdparty/squish/config.h
 +++ b/thirdparty/squish/config.h
 @@ -32,6 +32,26 @@
@@ -82,17 +94,19 @@ index 92edefe96..05f8d7259 100644
  #define SQUISH_USE_SSE 0
  #endif
 diff --git a/thirdparty/squish/squish.cpp b/thirdparty/squish/squish.cpp
-index 1d22a64ad..fd11a147d 100644
+index 1d22a64ad6..086ba11cd0 100644
 --- a/thirdparty/squish/squish.cpp
 +++ b/thirdparty/squish/squish.cpp
-@@ -135,7 +135,13 @@ void Decompress( u8* rgba, void const* block, int flags )
+@@ -135,7 +135,15 @@ void Decompress( u8* rgba, void const* block, int flags )
          colourBlock = reinterpret_cast< u8 const* >( block ) + 8;
  
      // decompress colour
 -    DecompressColour( rgba, colourBlock, ( flags & kDxt1 ) != 0 );
 +    // -- GODOT start --
 +    //DecompressColour( rgba, colourBlock, ( flags & kDxt1 ) != 0 );
-+    if(( flags & ( kBc5 ) ) != 0)
++    if(( flags & ( kBc4 ) ) != 0)
++        DecompressColourBc4( rgba, colourBlock);
++	else if(( flags & ( kBc5 ) ) != 0)
 +        DecompressColourBc5( rgba, colourBlock);
 +    else
 +        DecompressColour( rgba, colourBlock, ( flags & kDxt1 ) != 0 );

[akien-mga]

You missed the first chunk of my diff changing the style of the "Godot changes" comment at the top of thirdparty/squish/colourblock.cpp.

[YuriSizov]

Thanks!

[YuriSizov]

Cherry-picked for 4.2.2.