From b67126e917687a13c36a0177061dc8ad0a68f102 Mon Sep 17 00:00:00 2001
From: Stenzek <stenzek@gmail.com>
Date: Sun, 31 Dec 2023 00:04:14 +1000
Subject: [PATCH] GS/HW: Use DECAL/TCC for GT4 render fix

That way the channel gets actually written to alpha.
---
 pcsx2/GS/Renderers/HW/GSHwHack.cpp | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/pcsx2/GS/Renderers/HW/GSHwHack.cpp b/pcsx2/GS/Renderers/HW/GSHwHack.cpp
index 4ba3c7b196..eb9a16c50c 100644
--- a/pcsx2/GS/Renderers/HW/GSHwHack.cpp
+++ b/pcsx2/GS/Renderers/HW/GSHwHack.cpp
@@ -739,13 +739,21 @@ bool GSHwHack::GSC_PolyphonyDigitalGames(GSRendererHW& r, int& skip)
 					continue;
 			}
 
+			// Need the alpha channel.
 			dst->m_TEX0.PSM = PSMCT32;
+
+			// Alpha is unknown, since it comes from RGB.
+			dst->m_alpha_min = 0;
+			dst->m_alpha_max = 255;
+
 			dst->UpdateValidChannels(PSMCT32, fbmsk);
 			dst->UpdateValidity(GSVector4i::loadh(size));
 
 			GSHWDrawConfig& config = r.BeginHLEHardwareDraw(
 				dst->GetTexture(), nullptr, dst->GetScale(), src->GetTexture(), src->GetScale(), src->GetUnscaledRect());
 			config.pal = palette->GetPaletteGSTexture();
+			config.ps.tfx = TFX_DECAL;
+			config.ps.tcc = true;
 			config.ps.channel = ChannelFetch_RED + channel;
 			config.colormask.wrgba = 8;
 			r.EndHLEHardwareDraw(false);