From 8d32114d25e8bcb7bf4975ce0fa7a07343835bd1 Mon Sep 17 00:00:00 2001
From: Brett Gordon <beretta42@gmail.com>
Date: Tue, 15 Sep 2020 09:50:53 -0400
Subject: [PATCH] support returning color index and transparency of paletted
 images

---
 png.lua | 24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/png.lua b/png.lua
index 88fc38d..1b293d4 100644
--- a/png.lua
+++ b/png.lua
@@ -96,12 +96,23 @@ local function getDataPLTE(stream, length)
         data.colors[i] = {
             R = readByte(stream),
             G = readByte(stream),
-            B = readByte(stream)
+            B = readByte(stream),
+            A = 255
         }
     end
     return data
 end
 
+local function getDatatRNS(stream, length, palette)
+    local data = {}
+    data["numColors"] = length
+    data["colors"] = {}
+    for i = 1, length do
+        palette.colors[i].A = readByte(stream)
+    end
+    return data
+end
+
 local function extractChunkData(stream)
     local chunkData = {}
     local length
@@ -116,7 +127,9 @@ local function extractChunkData(stream)
         elseif (type == "IDAT") then
             chunkData[type] = getDataIDAT(stream, length, chunkData[type])
         elseif (type == "PLTE") then
-            chunkData[type] = getDataPLTE(stream, length)
+	    chunkData[type] = getDataPLTE(stream, length)
+	elseif (type == "tRNS") then
+	   chunkData[type] = getDatatRNS(stream, length, chunkData["PLTE"])
         else
             readChar(stream, length)
         end
@@ -128,7 +141,7 @@ end
 
 local function makePixel(stream, depth, colorType, palette)
     local bps = math.floor(depth/8) --bits per sample
-    local pixelData = { R = 0, G = 0, B = 0, A = 0 }
+    local pixelData = { R = 0, G = 0, B = 0, A = 0, I = 0 }
     local grey
     local index
     local color 
@@ -150,7 +163,8 @@ local function makePixel(stream, depth, colorType, palette)
         pixelData.R = color.R
         pixelData.G = color.G
         pixelData.B = color.B
-        pixelData.A = 255
+        pixelData.A = color.A
+        pixelData.I = index
     elseif colorType == 4 then
         grey = readInt(stream, bps)
         pixelData.R = grey
@@ -303,4 +317,4 @@ local function pngImage(path, progCallback, verbose, memSave)
     }
 end
 
-return pngImage
\ No newline at end of file
+return pngImage