From e5a598414fbf142d3f7c150b8bdb6856ea268218 Mon Sep 17 00:00:00 2001
From: LepkoQQ <lepko.san@gmail.com>
Date: Sun, 26 Apr 2020 20:02:30 +0200
Subject: [PATCH] LibGfx: PNGLoader support for grayscale images with alpha.

---
 Libraries/LibGfx/PNGLoader.cpp | 44 +++++++++++++++++++++++++++++++---
 1 file changed, 41 insertions(+), 3 deletions(-)

diff --git a/Libraries/LibGfx/PNGLoader.cpp b/Libraries/LibGfx/PNGLoader.cpp
index 9c4c686368..a7e64b8a9b 100644
--- a/Libraries/LibGfx/PNGLoader.cpp
+++ b/Libraries/LibGfx/PNGLoader.cpp
@@ -67,6 +67,18 @@ struct [[gnu::packed]] PaletteEntry
     //u8 a;
 };
 
+struct [[gnu::packed]] Tuple
+{
+    u8 gray;
+    u8 a;
+};
+
+struct [[gnu::packed]] Tuple16
+{
+    u16 gray;
+    u16 a;
+};
+
 struct [[gnu::packed]] Triplet
 {
     u8 r;
@@ -331,6 +343,33 @@ template<bool has_alpha, u8 filter_type>
             ASSERT_NOT_REACHED();
         }
         break;
+    case 4:
+        if (context.bit_depth == 8) {
+            for (int y = 0; y < context.height; ++y) {
+                auto* tuples = (Tuple*)context.scanlines[y].data.data();
+                for (int i = 0; i < context.width; ++i) {
+                    auto& pixel = (Pixel&)context.bitmap->scanline(y)[i];
+                    pixel.r = tuples[i].gray;
+                    pixel.g = tuples[i].gray;
+                    pixel.b = tuples[i].gray;
+                    pixel.a = tuples[i].a;
+                }
+            }
+        } else if (context.bit_depth == 16) {
+            for (int y = 0; y < context.height; ++y) {
+                auto* tuples = (Tuple16*)context.scanlines[y].data.data();
+                for (int i = 0; i < context.width; ++i) {
+                    auto& pixel = (Pixel&)context.bitmap->scanline(y)[i];
+                    pixel.r = tuples[i].gray & 0xFF;
+                    pixel.g = tuples[i].gray & 0xFF;
+                    pixel.b = tuples[i].gray & 0xFF;
+                    pixel.a = tuples[i].a & 0xFF;
+                }
+            }
+        } else {
+            ASSERT_NOT_REACHED();
+        }
+        break;
     case 2:
         if (context.bit_depth == 8) {
             for (int y = 0; y < context.height; ++y) {
@@ -617,9 +656,8 @@ static bool process_IHDR(const ByteBuffer& data, PNGLoadingContext& context, boo
         context.bytes_per_pixel = ihdr.bit_depth / 8;
         break;
     case 4: // Each pixel is a grayscale sample, followed by an alpha sample.
-        // FIXME: Implement grayscale PNG support.
-        dbgprintf("PNGLoader::process_IHDR: Unsupported grayscale format.\n");
-        return false;
+        context.bytes_per_pixel = 2 * ihdr.bit_depth / 8;
+        break;
     case 2:
         context.bytes_per_pixel = 3 * (ihdr.bit_depth / 8);
         break;