[librptexture] ICO: Handle Win3.x 1bpp (monochrome) icons.

Tested by converting Win2.x BANG.ICO to Win3.x format.

ICOPrivate::loadImage_Win1():
- Note that the mask is *before* the icon.

ImageDecoder::fromLinearMono_WinIcon():
- Take separate pointers for the icon and mask data. Win3.x icons are
  typically stored upside-down, so this lets us handle that outside
  of the decoder function. This also means the image data size does
  not have to be 2x. Note that `img_siz == mask_siz` must be true.

src/librptexture/decoder/ImageDecoder_Linear_Gray.cpp

@@ -190,29 +190,33 @@ rp_image_ptr fromLinearGray2bpp(int width, int height,
  * Convert a linear monochrome image to rp_image.
  *
  * Windows icons are handled a bit different compared to "regular" monochrome images:
- * - Actual image height should be double the `height` value.
- * - Two images are stored: mask, then image.
+ * - Two images are required: icon and mask
  * - Transparency is supported using the mask.
  * - 0 == black; 1 == white
  *
  * @param width		[in] Image width
  * @param height	[in] Image height
  * @param img_buf	[in] Monochrome image buffer
- * @param img_siz	[in] Size of image data [must be >= ((w*h)/8)*2]
+ * @param img_siz	[in] Size of image data [must be >= ((w*h)/8)]
+ * @param mask_buf	[in] Mask buffer
+ * @param mask_siz	[in] Size of mask buffer [must be == img_siz]
  * @param stride	[in,opt] Stride, in bytes (if 0, assumes width*bytespp)
  * @return rp_image, or nullptr on error.
  */
 ATTR_ACCESS_SIZE(read_only, 3, 4)
 rp_image_ptr fromLinearMono_WinIcon(int width, int height,
-	const uint8_t *RESTRICT img_buf, size_t img_siz, int stride)
+	const uint8_t *RESTRICT img_buf, size_t img_siz,
+	const uint8_t *RESTRICT mask_buf, size_t mask_siz, int stride)
 {
 	// Verify parameters.
 	assert(img_buf != nullptr);
 	assert(width > 0);
 	assert(height > 0);
-	assert(img_siz >= (static_cast<size_t>(width) * static_cast<size_t>(height) / 8) * 2);
+	assert(img_siz >= (static_cast<size_t>(width) * static_cast<size_t>(height) / 8));
+	assert(img_siz == mask_siz);
 	if (!img_buf || width <= 0 || height <= 0 ||
-	    img_siz < (static_cast<size_t>(width) * static_cast<size_t>(height) / 8) * 2)
+	    img_siz < (static_cast<size_t>(width) * static_cast<size_t>(height) / 8) ||
+	    img_siz != mask_siz)
 	{
 		return {};
 	}
@@ -247,12 +251,10 @@ rp_image_ptr fromLinearMono_WinIcon(int width, int height,
 
 	// Convert one line at a time. (monochrome -> CI8)
 	uint8_t *px_dest = static_cast<uint8_t*>(img->bits());
-	const uint8_t *mask_buf = img_buf;
-	const uint8_t *icon_buf = img_buf + (static_cast<size_t>(height) * static_cast<size_t>(stride));
 	for (unsigned int y = static_cast<unsigned int>(height); y > 0; y--) {
 		for (int x = width; x > 0; x -= 8) {
 			uint8_t pxMask = *mask_buf++;
-			uint8_t pxIcon = *icon_buf++;
+			uint8_t pxIcon = *img_buf++;
 
 			// For images where width is not a multiple of 8,
 			// we'll discard the remaining bits in the last byte.
@@ -281,6 +283,7 @@ rp_image_ptr fromLinearMono_WinIcon(int width, int height,
 	// Set the sBIT metadata.
 	// NOTE: Setting the grayscale value, though we're
 	// not saving grayscale PNGs at the moment.
+	// TODO: Don't set alpha if the icon mask doesn't have any set bits?
 	static const rp_image::sBIT_t sBIT = {1,1,1,1,1};
 	img->set_sBIT(&sBIT);
 

src/librptexture/decoder/ImageDecoder_Linear_Gray.hpp

@@ -49,20 +49,23 @@ rp_image_ptr fromLinearGray2bpp(int width, int height,
  * Convert a linear monochrome image to rp_image.
  *
  * Windows icons are handled a bit different compared to "regular" monochrome images:
- * - Actual image height should be double the `height` value.
- * - Two images are stored: mask, then image.
+ * - Two images are required: icon and mask
  * - Transparency is supported using the mask.
  * - 0 == black; 1 == white
  *
  * @param width		[in] Image width
  * @param height	[in] Image height
  * @param img_buf	[in] Monochrome image buffer
- * @param img_siz	[in] Size of image data [must be >= ((w*h)/8)*2]
+ * @param img_siz	[in] Size of image data [must be >= ((w*h)/8)]
+ * @param mask_buf	[in] Mask buffer
+ * @param mask_siz	[in] Size of mask buffer [must be == img_siz]
  * @param stride	[in,opt] Stride, in bytes (if 0, assumes width*bytespp)
  * @return rp_image, or nullptr on error.
  */
 ATTR_ACCESS_SIZE(read_only, 3, 4)
+ATTR_ACCESS_SIZE(read_only, 5, 6)
 rp_image_ptr fromLinearMono_WinIcon(int width, int height,
-	const uint8_t *RESTRICT img_buf, size_t img_siz, int stride = 0);
+	const uint8_t *RESTRICT img_buf, size_t img_siz,
+	const uint8_t *RESTRICT mask_buf, size_t mask_siz, int stride = 0);
 
 } }

src/librptexture/fileformat/ICO.cpp

@@ -504,7 +504,7 @@ int ICOPrivate::loadIconDirectory_Win3(void)
 rp_image_const_ptr ICOPrivate::loadImage_Win1(void)
 {
 	// Icon data is located immediately after the header.
-	// Each icon is actually two icons: a 1bpp icon, then a 1bpp mask.
+	// Each icon is actually two icons: a 1bpp mask, then a 1bpp icon.
 
 	// NOTE: If the file has *both* DIB and DDB, then the DIB is first,
 	// followed by the DDB, with its own icon header. Not handling this
@@ -546,7 +546,10 @@ rp_image_const_ptr ICOPrivate::loadImage_Win1(void)
 	}
 
 	// Convert the icon.
-	img = ImageDecoder::fromLinearMono_WinIcon(width, height, icon_data.data(), icon_size * 2, stride);
+	const uint8_t *const p_mask_data = icon_data.data();
+	const uint8_t *const p_icon_data = p_mask_data + icon_size;
+	img = ImageDecoder::fromLinearMono_WinIcon(width, height,
+		p_icon_data, icon_size, p_mask_data, icon_size, stride);
 	return img;
 }
 
@@ -718,9 +721,12 @@ rp_image_const_ptr ICOPrivate::loadImage_Win3(void)
 			return {};
 
 		case 1:
-			// Monochrome (TODO: Find a test icon)
-			assert(!"Win3.x 1bpp icon format is not supported yet!");
-			return {};
+			// 1bpp (monochrome)
+			// NOTE: ImageDecoder::fromLinearMono_WinIcon() handles the mask.
+			img = ImageDecoder::fromLinearMono_WinIcon(width, half_height,
+				icon_data, icon_size,
+				mask_data, mask_size, stride);
+			break;
 
 		case 4:
 			// 16-color
@@ -760,7 +766,9 @@ rp_image_const_ptr ICOPrivate::loadImage_Win3(void)
 	// Apply the icon mask.
 	rp_image::sBIT_t sBIT;
 	img->get_sBIT(&sBIT);
-	if (bitcount < 8) {
+	if (bitcount == 1) {
+		// Monochrome icons are handled by ImageDecoder::fromLinearMono_WinIcon().
+	} else if (bitcount < 8) {
 		// Keep the icon as CI8 and add a transparency color.
 		// TODO: Set sBIT.
 		assert(img->format() == rp_image::Format::CI8);