From 4d3227b604e1805f74c00691c76569fa8df90e7d Mon Sep 17 00:00:00 2001
From: Mihir <mihirsuks@gmail.com>
Date: Sun, 2 May 2021 11:08:16 -0500
Subject: [PATCH] Add flip vertical feature on decode

---
 docs/decode.md | 1 +
 spng/spng.c    | 5 +++++
 spng/spng.h    | 1 +
 3 files changed, 7 insertions(+)

diff --git a/docs/decode.md b/docs/decode.md
index f7efc6b4..e3a7b5d6 100644
--- a/docs/decode.md
+++ b/docs/decode.md
@@ -40,6 +40,7 @@ enum spng_decode_flags
 
     SPNG_DECODE_TRNS = 1, /* Apply transparency */
     SPNG_DECODE_GAMMA = 2, /* Apply gamma correction */
+    SPNG_DECODE_FLIP_Y = 16, /* Flip the image vertically */
     SPNG_DECODE_PROGRESSIVE = 256 /* Initialize for progressive reads */
 };
 ```
diff --git a/spng/spng.c b/spng/spng.c
index 8d459e18..a8076dd5 100644
--- a/spng/spng.c
+++ b/spng/spng.c
@@ -3216,6 +3216,11 @@ int spng_decode_image(spng_ctx *ctx, void *out, size_t len, int fmt, int flags)
     {
         size_t ioffset = ri->row_num * ctx->out_width;
 
+        if(flags & SPNG_DECODE_FLIP_Y)
+        {
+            ioffset = len - ctx->out_width - ioffset;
+        }
+
         ret = spng_decode_row(ctx, (unsigned char*)out + ioffset, ctx->out_width);
     }while(!ret);
 
diff --git a/spng/spng.h b/spng/spng.h
index e89bd7cd..2de477f8 100644
--- a/spng/spng.h
+++ b/spng/spng.h
@@ -172,6 +172,7 @@ enum spng_decode_flags
 
     SPNG_DECODE_TRNS = 1, /* Apply transparency */
     SPNG_DECODE_GAMMA = 2, /* Apply gamma correction */
+    SPNG_DECODE_FLIP_Y = 16, /* Flip the image vertically */
     SPNG_DECODE_PROGRESSIVE = 256 /* Initialize for progressive reads */
 };