IMG-25: load ICO files (#1458)

* disk_sink + fixes

* Always 4 bands for v3+ bmp on save

* bmpsave fixed (w/o orientation)

* fixed ico for target save

* icosave.c

* Removed leftover comments

* icoload.c

* Row buffer (skripatch) is not needed anymore

* Minor fixes for icoload/save

* Use wips_image_write instead of vips_copy

* Forgotten &

* Check resulting dimensions

* -debug printf

vips/ico.h

@@ -1,10 +1,40 @@
 /*
- * ICO save/load
+ * ICO save/load. ICO is a container for one+ PNG/BMP images.
  */
 #ifndef __ICO_H__
 #define __ICO_H__
 
+#include <stdint.h>
+
+#define ICO_TYPE_ICO 1
+#define ICO_TYPE_CURSOR 2
+
+// ICO file header
+typedef struct __attribute__((packed)) _ICONDIR_IcoHeader {
+  uint16_t reserved;    // Reserved, always 0
+  uint16_t type;        // 1 for ICO, 2 for CUR
+  uint16_t image_count; // Number of images in the file
+} ICONDIR_IcoHeader;
+
+// ICO image header
+typedef struct __attribute__((packed)) _ICONDIRENTRY_IcoHeader {
+  uint8_t width;            // Width of the icon in pixels (0 for 256)
+  uint8_t height;           // Height of the icon in pixels (0 for 256
+  uint8_t number_of_colors; // Number of colors, not used in our case
+  uint8_t reserved;         // Reserved, always 0
+  uint16_t color_planes;    // Color planes, always 1
+  uint16_t bpp;             // Bits per pixel
+  uint32_t data_size;       // Image data size
+  uint32_t data_offset;     // Image data offset, always 22
+} ICONDIRENTRY_IcoHeader;
+
 // defined in icosave.c
 int vips_icosave_target_go(VipsImage *in, VipsTarget *target);
 
+// defined in icoload.c
+VIPS_API
+int icoload_source(VipsSource *source, VipsImage **out, ...)
+    G_GNUC_NULL_TERMINATED;
+int vips_icoload_source_go(VipsImgproxySource *source, VipsImage **out);
+
 #endif