Use imageIndex to calculate height/width and buffer offset.

imageio/imageio-dds/src/main/java/com/twelvemonkeys/imageio/plugins/dds/DDSHeader.java

@@ -2,18 +2,18 @@ package com.twelvemonkeys.imageio.plugins.dds;
 
 import javax.imageio.IIOException;
 import javax.imageio.stream.ImageInputStream;
+import java.awt.Dimension;
 import java.io.IOException;
 import java.math.BigInteger;
-import java.nio.ByteOrder;
 import java.util.Arrays;
 
 final class DDSHeader {
 
     // https://learn.microsoft.com/en-us/windows/win32/direct3ddds/dx-graphics-dds-pguide
     private int flags;
-    private int width;
-    private int height;
-    private int mipmap;
+
+    private int mipMapCount;
+    private Dimension[] dimensions;
 
     private int pixelFormatFlags;
     private int fourCC;
@@ -25,7 +25,7 @@ final class DDSHeader {
 
     public static DDSHeader read(final ImageInputStream imageInput) throws IOException {
         DDSHeader header = new DDSHeader();
-        
+
         // Read MAGIC bytes [0,3]
         byte[] magic = new byte[DDS.MAGIC.length];
         imageInput.readFully(magic);
@@ -50,13 +50,15 @@ final class DDSHeader {
         }
 
         // Read Height & Width
-        header.height = imageInput.readInt(); // [12,15]
-        header.width = imageInput.readInt();  // [16,19]
-
+        int dwHeight = imageInput.readInt(); // [12,15]
+        int dwWidth = imageInput.readInt();  // [16,19]
 
         int dwPitchOrLinearSize = imageInput.readInt(); // [20,23]
         int dwDepth = imageInput.readInt(); // [24,27]
-        header.mipmap = imageInput.readInt(); // [28,31]
+        header.mipMapCount = imageInput.readInt(); // [28,31]
+
+        // build dimensions list
+        header.addDimensions(dwWidth, dwHeight);
 
         byte[] dwReserved1 = new byte[11 * 4];  // [32,75]
         imageInput.readFully(dwReserved1);
@@ -82,28 +84,35 @@ final class DDSHeader {
         return header;
     }
 
+    private void addDimensions(int width, int height) {
+        dimensions = new Dimension[getMipMapCount()];
+
+        int w = width;
+        int h = height;
+        for (int i = 0; i < getMipMapCount(); i++) {
+            dimensions[i] = new Dimension(w, h);
+            w /= 2;
+            h /= 2;
+        }
+    }
+
     private boolean getFlag(int mask) {
         return (flags & mask) != 0;
     }
 
-    public int getWidth() {
-        return width;
+    public int getWidth(int imageIndex) {
+        int lim = dimensions[imageIndex].width;
+        return (lim <= 0) ? 1 : lim;
     }
 
-    public void setWidth(int width) {
-        this.width = width;
+    public int getHeight(int imageIndex) {
+        int lim =  dimensions[imageIndex].height;
+        return (lim <= 0) ? 1 : lim;
     }
 
-    public int getHeight() {
-        return height;
-    }
-
-    public void setHeight(int height) {
-        this.height = height;
-    }
-
-    public int getMipmap() {
-        return mipmap;
+    public int getMipMapCount() {
+        // 0 = (unused) or 1 = (1 level), but still only one 'base' image
+        return (mipMapCount == 0) ? 1 : mipMapCount;
     }
 
     public int getAlphaMask() {

imageio/imageio-dds/src/main/java/com/twelvemonkeys/imageio/plugins/dds/DDSImageReader.java

@@ -34,7 +34,7 @@ public final class DDSImageReader extends ImageReaderBase {
         checkBounds(imageIndex);
         readHeader();
 
-        return header.getWidth();
+        return header.getWidth(imageIndex);
     }
 
     @Override
@@ -42,7 +42,14 @@ public final class DDSImageReader extends ImageReaderBase {
         checkBounds(imageIndex);
         readHeader();
 
-        return header.getHeight();
+        return header.getHeight(imageIndex);
+    }
+
+    @Override
+    public int getNumImages(final boolean allowSearch) throws IOException {
+        readHeader();
+
+        return header.getMipMapCount();
     }
 
     @Override

imageio/imageio-dds/src/main/java/com/twelvemonkeys/imageio/plugins/dds/DDSReader.java

@@ -29,39 +29,21 @@ final class DDSReader {
         this.header = header;
     }
 
-    public int[] read(ImageInputStream imageInput, int mipmapLevel) throws IOException {
-
-        // header
-        int width = header.getWidth();
-        int height = header.getHeight();
-        int mipmap = header.getMipmap();
-
-        if (mipmapLevel > mipmap) {
-            throw new IIOException("Invalid mipmap level: " + mipmapLevel);
-        }
+    public int[] read(ImageInputStream imageInput, int imageIndex) throws IOException {
 
         // type
         DDSType type = getType();
 
-        // length
-        int len = getLength(type, width, height);
-        byte[] buffer = new byte[len];
-        imageInput.readFully(buffer);
-
-        for (int i = 1; i < mipmapLevel; i++) {
-            width /= 2;
-            height /= 2;
-
-            // length
-            len = getLength(type, width, height);
+        // offset buffer to index mipmap image
+        byte[] buffer = null;
+        for (int i = 0; i <= imageIndex; i++) {
+            int len = getLength(type, i);
             buffer = new byte[len];
             imageInput.readFully(buffer);
         }
-        if (width <= 0) width = 1;
-        if (height <= 0) height = 1;
 
-        header.setWidth(width);
-        header.setHeight(height);
+        int width = header.getWidth(imageIndex);
+        int height = header.getHeight(imageIndex);
 
         switch (type) {
             case DXT1:
@@ -163,7 +145,10 @@ final class DDSReader {
         }
     }
 
-    private static int getLength(DDSType type, int width, int height) throws IIOException {
+    private int getLength(DDSType type, int imageIndex) throws IIOException {
+        int width = header.getWidth(imageIndex);
+        int height = header.getHeight(imageIndex);
+
         switch (type) {
             case DXT1:
                 return 8 * ((width + 3) / 4) * ((height + 3) / 4);