From 2ea8a9ac1fa06a955290928f11770964fa7798cd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Henrik=20Rydg=C3=A5rd?= <hrydgard@gmail.com>
Date: Wed, 3 Jun 2026 17:17:54 +0200
Subject: [PATCH] Revert "Remove unnecessary scaling and then un-scaling of
 through-mode Z coordinates"

Didn't mean to commit this, it was supposed to go in a PR.

This reverts commit 6d4c70c67d7ccc3fdd3f6210349ab43e5ab19550.
---
 GPU/Common/VertexDecoderCommon.h     | 10 ++++++++--
 GPU/Common/VertexShaderGenerator.cpp | 10 +++++++---
 GPU/Software/TransformUnit.cpp       |  3 ++-
 3 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/GPU/Common/VertexDecoderCommon.h b/GPU/Common/VertexDecoderCommon.h
index f819ea363c..696eee018d 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];
+			pos[2] = (int)f[2] * (1.0f / 65535.0f);
 		}
 	}
 
@@ -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];
+		pos[2] = (int)f[2] * (1.0f / 65535.0f);
 	}
 
 	void ReadPosNonThrough(float pos[3]) const {
@@ -153,6 +153,12 @@ 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 b4694db13b..0170593798 100644
--- a/GPU/Common/VertexShaderGenerator.cpp
+++ b/GPU/Common/VertexShaderGenerator.cpp
@@ -760,9 +760,13 @@ bool GenerateVertexShader(const VShaderID &id, char *buffer, const ShaderLanguag
 			}
 		}
 		WRITE(p, "  %sv_fogdepth = fog;\n", compat.vsOutPrefix);
-
-		// If non-through, the viewport has already been applied here.
-		WRITE(p, "  vec4 outPos = position;\n");
+		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 (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 92a8a6c1e6..853a3ce4a2 100644
--- a/GPU/Software/TransformUnit.cpp
+++ b/GPU/Software/TransformUnit.cpp
@@ -350,7 +350,8 @@ ClipVertexData TransformUnit::ReadVertex(const VertexReader &vreader, const Tran
 	ClipVertexData vertex;
 
 	ModelCoords pos;
-	vreader.ReadPosThrough(pos.AsArray());
+	// VertexDecoder normally scales z, but we want it unscaled.
+	vreader.ReadPosThroughZ16(pos.AsArray());
 
 	static Vec3Packedf lastTC;
 	if (state.readUV) {