From a9caeaa7f1f730cb0c63cea22b30aae8d7f1b3f9 Mon Sep 17 00:00:00 2001
From: Jonathan G Rennison <j.g.rennison@gmail.com>
Date: Thu, 19 May 2022 00:09:14 +0100
Subject: [PATCH] Fix viewport map scrolling box blend on emscripten

---
 src/viewport.cpp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/viewport.cpp b/src/viewport.cpp
index 3dbf20e542..8eb6345d1d 100644
--- a/src/viewport.cpp
+++ b/src/viewport.cpp
@@ -3127,6 +3127,10 @@ uint32 ViewportMapGetColour(const Viewport * const vp, int x, int y, const uint
 /* Taken from http://stereopsis.com/doubleblend.html, PixelBlend() is faster than ComposeColourRGBANoCheck() */
 static inline void PixelBlend(uint32 * const d, const uint32 s)
 {
+#if defined(__EMSCRIPTEN__)
+	*d = Blitter_32bppBase::ComposeColourRGBANoCheck(s & 0xFF, (s >> 8) & 0xFF, (s >> 16) & 0xFF, (s >> 24) & 0xFF, Colour(*d)).data;
+	return;
+#endif
 	const uint32 a     = (s >> 24) + 1;
 	const uint32 dstrb = *d & 0xFF00FF;
 	const uint32 dstg  = *d & 0xFF00;