From f5494d9acf986e9cd86f3ae5d3bad4b0d1549f26 Mon Sep 17 00:00:00 2001
From: Kai Uwe Broulik <kde@privat.broulik.de>
Date: Sun, 6 Jul 2025 16:13:50 +0200
Subject: [PATCH] iff: Support ILBM (PBM)

It's another variant of IFF where the pixel data is stored
contiguously rather than interleaved.
---
 src/imageformats/chunks.cpp | 24 +++++++++++++++++-------
 src/imageformats/chunks_p.h | 17 ++++++++++++-----
 src/imageformats/iff.cpp    |  6 +++---
 src/imageformats/iff.json   |  4 ++--
 4 files changed, 34 insertions(+), 17 deletions(-)

diff --git a/src/imageformats/chunks.cpp b/src/imageformats/chunks.cpp
index 6344ca9..df15fd6 100644
--- a/src/imageformats/chunks.cpp
+++ b/src/imageformats/chunks.cpp
@@ -547,9 +547,9 @@ bool BODYChunk::isValid() const
     return chunkId() == BODYChunk::defaultChunkId();
 }
 
-QByteArray BODYChunk::strideRead(QIODevice *d, const BMHDChunk *header, const CAMGChunk *camg, const CMAPChunk *cmap) const
+QByteArray BODYChunk::strideRead(QIODevice *d, const FORMChunk *form, const BMHDChunk *header, const CAMGChunk *camg, const CMAPChunk *cmap) const
 {
-    if (!isValid() || header == nullptr) {
+    if (!isValid() || form == nullptr || header == nullptr) {
         return {};
     }
 
@@ -571,7 +571,11 @@ QByteArray BODYChunk::strideRead(QIODevice *d, const BMHDChunk *header, const CA
 
     auto planes = _readBuffer.left(readSize);
     _readBuffer.remove(0, readSize);
-    return BODYChunk::deinterleave(planes, header, camg, cmap);
+    if (form->formType() == FORMChunk::FormType::Pbm) {
+        return planes;
+    } else {
+        return BODYChunk::deinterleave(planes, header, camg, cmap);
+    }
 }
 
 bool BODYChunk::resetStrideRead(QIODevice *d) const
@@ -773,15 +777,21 @@ bool FORMChunk::innerReadStructure(QIODevice *d)
     if (bytes() < 4) {
         return false;
     }
-    _type = d->read(4);
-    auto ok = true;
-    if (_type == QByteArray("ILBM")) {
+    const auto type = d->read(4);
+    auto ok = false;
+    if (type == QByteArrayLiteral("ILBM")) {
+        _type = FormType::Ilbm;
+    } else if (type == QByteArrayLiteral("PBM ")) {
+        _type = FormType::Pbm;
+    }
+
+    if (_type != FormType::Unknown) {
         setChunks(IFFChunk::innerFromDevice(d, &ok, alignBytes(), recursionCounter()));
     }
     return ok;
 }
 
-QByteArray FORMChunk::formType() const
+FORMChunk::FormType FORMChunk::formType() const
 {
     return _type;
 }
diff --git a/src/imageformats/chunks_p.h b/src/imageformats/chunks_p.h
index c77deaa..69f42d9 100644
--- a/src/imageformats/chunks_p.h
+++ b/src/imageformats/chunks_p.h
@@ -451,6 +451,7 @@ protected:
     virtual bool innerReadStructure(QIODevice *d) override;
 };
 
+class FORMChunk;
 
 /*!
  * \brief The BODYChunk class
@@ -476,7 +477,7 @@ public:
      * \return The scanline as requested for QImage.
      * \warning Call resetStrideRead() once before this one.
      */
-    QByteArray strideRead(QIODevice *d, const BMHDChunk *header, const CAMGChunk *camg = nullptr, const CMAPChunk *cmap = nullptr) const;
+    QByteArray strideRead(QIODevice *d, const FORMChunk *form, const BMHDChunk *header, const CAMGChunk *camg = nullptr, const CMAPChunk *cmap = nullptr) const;
 
     /*!
      * \brief resetStrideRead
@@ -500,9 +501,13 @@ private:
  */
 class FORMChunk : public IFFChunk
 {
-    QByteArray _type;
-
 public:
+    enum class FormType {
+        Unknown,
+        Ilbm,
+        Pbm,
+    };
+
     virtual ~FORMChunk() override;
     FORMChunk();
     FORMChunk(const FORMChunk& other) = default;
@@ -512,7 +517,7 @@ public:
 
     bool isSupported() const;
 
-    QByteArray formType() const;
+    FormType formType() const;
 
     QImage::Format format() const;
 
@@ -522,8 +527,10 @@ public:
 
 protected:
     virtual bool innerReadStructure(QIODevice *d) override;
-};
 
+private:
+    FormType _type = FormType::Unknown;
+};
 
 /*!
  * \brief The FOR4Chunk class
diff --git a/src/imageformats/iff.cpp b/src/imageformats/iff.cpp
index 2ffed32..f4a1d96 100644
--- a/src/imageformats/iff.cpp
+++ b/src/imageformats/iff.cpp
@@ -74,7 +74,7 @@ IFFHandler::IFFHandler()
 bool IFFHandler::canRead() const
 {
     if (canRead(device())) {
-        setFormat("iff");
+        setFormat("iff"); // TODO ilbm based on header?
         return true;
     }
     return false;
@@ -192,7 +192,7 @@ bool IFFHandler::readStandardImage(QImage *image)
         }
         for (auto y = 0, h = img.height(); y < h; ++y) {
             auto line = reinterpret_cast<char*>(img.scanLine(y));
-            auto ba = body->strideRead(device(), header, camg, cmap);
+            auto ba = body->strideRead(device(), form, header, camg, cmap);
             if (ba.isEmpty()) {
                 qCWarning(LOG_IFFPLUGIN) << "IFFHandler::readStandardImage() error while reading image scanline";
                 return false;
@@ -334,7 +334,7 @@ QVariant IFFHandler::option(ImageOption option) const
 
 QImageIOPlugin::Capabilities IFFPlugin::capabilities(QIODevice *device, const QByteArray &format) const
 {
-    if (format == "iff") {
+    if (format == "iff" || format == "ilbm") {
         return Capabilities(CanRead);
     }
     if (!format.isEmpty()) {
diff --git a/src/imageformats/iff.json b/src/imageformats/iff.json
index a64b8cb..f1ea9d4 100644
--- a/src/imageformats/iff.json
+++ b/src/imageformats/iff.json
@@ -1,4 +1,4 @@
 {
-    "Keys": [ "iff" ],
-    "MimeTypes": [ "application/x-iff" ]
+    "Keys": [ "iff", "ilbm" ],
+    "MimeTypes": [ "application/x-iff", "application/x-ilbm" ]
 }