From 6d4c70c67d7ccc3fdd3f6210349ab43e5ab19550 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Henrik=20Rydg=C3=A5rd?= <hrydgard@gmail.com>
Date: Wed, 3 Jun 2026 15:59:36 +0200
Subject: [PATCH] Remove unnecessary scaling and then un-scaling of
 through-mode Z coordinates

---
 GPU/Common/VertexDecoderCommon.h     | 10 ++--------
 GPU/Common/VertexShaderGenerator.cpp | 10 +++-------
 GPU/Software/TransformUnit.cpp       |  3 +--
 3 files changed, 6 insertions(+), 17 deletions(-)

diff --git a/GPU/Common/VertexDecoderCommon.h b/GPU/Common/VertexDecoderCommon.h
index 696eee018d..f819ea363c 100644
--- a/GPU/Common/VertexDecoderCommon.h
+++ b/GPU/Common/VertexDecoderCommon.h
@@ -134,7 +134,7 @@ public:
 			pos[2] = f[2];
 		} else {
 			// Integer value passed in a float. Clamped to 0, 65535.
-			pos[2] = (int)f[2] * (1.0f / 65535.0f);
+			pos[2] = (int)f[2];
 		}
 	}
 
@@ -144,7 +144,7 @@ public:
 		pos[0] = f[0];
 		pos[1] = f[1];
 		// Integer value passed in a float. Clamped to 0, 65535.
-		pos[2] = (int)f[2] * (1.0f / 65535.0f);
+		pos[2] = (int)f[2];
 	}
 
 	void ReadPosNonThrough(float pos[3]) const {
@@ -153,12 +153,6 @@ public:
 		memcpy(pos, f, 12);
 	}
 
-	void ReadPosThroughZ16(float pos[3]) const {
-		// Only DEC_FLOAT_3 is supported.
-		const float *f = (const float *)(data_ + decFmt_.posoff);
-		memcpy(pos, f, 12);
-	}
-
 	void ReadNrm(float nrm[3]) const {
 		switch (decFmt_.nrmfmt) {
 		case DEC_FLOAT_3:
diff --git a/GPU/Common/VertexShaderGenerator.cpp b/GPU/Common/VertexShaderGenerator.cpp
index 0170593798..b4694db13b 100644
--- a/GPU/Common/VertexShaderGenerator.cpp
+++ b/GPU/Common/VertexShaderGenerator.cpp
@@ -760,13 +760,9 @@ bool GenerateVertexShader(const VShaderID &id, char *buffer, const ShaderLanguag
 			}
 		}
 		WRITE(p, "  %sv_fogdepth = fog;\n", compat.vsOutPrefix);
-		if (isModeThrough)	{
-			WRITE(p, "  vec4 outPos = position;\n");
-			WRITE(p, "  outPos.z *= 65536.0;\n");  // TODO: This multiplication should be moved to the vertex decoders for through mode.
-		} else {
-			// The viewport has already been applied here, along with the division.
-			WRITE(p, "  vec4 outPos = position;\n");
-		}
+
+		// If non-through, the viewport has already been applied here.
+		WRITE(p, "  vec4 outPos = position;\n");
 
 		if (fsMinmaxDiscard || fsDepthClamp) {
 			WRITE(p, "  %sv_zw = vec2(outPos.z * outPos.w, outPos.w);\n", compat.vsOutPrefix);
diff --git a/GPU/Software/TransformUnit.cpp b/GPU/Software/TransformUnit.cpp
index 853a3ce4a2..92a8a6c1e6 100644
--- a/GPU/Software/TransformUnit.cpp
+++ b/GPU/Software/TransformUnit.cpp
@@ -350,8 +350,7 @@ ClipVertexData TransformUnit::ReadVertex(const VertexReader &vreader, const Tran
 	ClipVertexData vertex;
 
 	ModelCoords pos;
-	// VertexDecoder normally scales z, but we want it unscaled.
-	vreader.ReadPosThroughZ16(pos.AsArray());
+	vreader.ReadPosThrough(pos.AsArray());
 
 	static Vec3Packedf lastTC;
 	if (state.readUV) {