GS-hw, TC: fix tex scaling for native res draws.

The GSTextureCache::ScaleTexture method did not work
correctly when an old texture with a scale factor
different from 1 was recycled for a draw which was forced at
native resolution (the old scale factor was kept).

pcsx2/GS/Renderers/Common/GSRenderer.h

@@ -60,6 +60,7 @@ public:
 	virtual bool CanUpscale() { return false; }
 	virtual int GetUpscaleMultiplier() { return 1; }
 	virtual GSVector2i GetCustomResolution() { return GSVector2i(0, 0); }
+	virtual GSVector2 GetTextureScaleFactor() { return { 1.0f, 1.0f }; }
 	GSVector2i GetInternalResolution();
 	void SetVSync(int vsync);
 

pcsx2/GS/Renderers/HW/GSRendererHW.cpp

@@ -775,6 +775,29 @@ void GSRendererHW::MergeSprite(GSTextureCache::Source* tex)
 	}
 }
 
+GSVector2 GSRendererHW::GetTextureScaleFactor()
+{
+	GSVector2 scale_factor{ 1.0f, 1.0f };
+	if (CanUpscale())
+	{
+		const int multiplier = GetUpscaleMultiplier();
+		if (multiplier == 0)
+		{
+			// Custom resolution.
+			const GSVector4i display_rect = GetDisplayRect();
+			const GSVector2i requested_resolution = GetCustomResolution();
+			scale_factor.x = static_cast<float>(requested_resolution.x) / display_rect.width();
+			scale_factor.y = static_cast<float>(requested_resolution.y) / display_rect.height();
+		}
+		else
+		{
+			scale_factor.x = multiplier;
+			scale_factor.y = multiplier;
+		}
+	}
+	return scale_factor;
+}
+
 void GSRendererHW::InvalidateVideoMem(const GIFRegBITBLTBUF& BITBLTBUF, const GSVector4i& r)
 {
 	// printf("[%d] InvalidateVideoMem %d,%d - %d,%d %05x (%d)\n", (int)m_perfmon.GetFrame(), r.left, r.top, r.right, r.bottom, (int)BITBLTBUF.DBP, (int)BITBLTBUF.DPSM);

pcsx2/GS/Renderers/HW/GSRendererHW.h

@@ -179,6 +179,7 @@ public:
 	GSVector4 RealignTargetTextureCoordinate(const GSTextureCache::Source* tex);
 	GSVector4i ComputeBoundingBox(const GSVector2& rtscale, const GSVector2i& rtsize);
 	void MergeSprite(GSTextureCache::Source* tex);
+	GSVector2 GetTextureScaleFactor();
 
 	void Reset();
 	void VSync(int field);

pcsx2/GS/Renderers/HW/GSTextureCache.cpp

@@ -498,24 +498,8 @@ GSTextureCache::Source* GSTextureCache::LookupSource(const GIFRegTEX0& TEX0, con
 
 void GSTextureCache::ScaleTexture(GSTexture* texture)
 {
-	if (!m_renderer->CanUpscale())
+	if (texture)
-		return;
+		texture->SetScale(m_renderer->GetTextureScaleFactor());
-
-	float multiplier = static_cast<float>(m_renderer->GetUpscaleMultiplier());
-	bool custom_resolution = (multiplier == 0);
-	GSVector2 scale_factor(multiplier);
-
-	if (custom_resolution)
-	{
-		int width = m_renderer->GetDisplayRect().width();
-		int height = m_renderer->GetDisplayRect().height();
-
-		GSVector2i requested_resolution = m_renderer->GetCustomResolution();
-		scale_factor.x = static_cast<float>(requested_resolution.x) / width;
-		scale_factor.y = static_cast<float>(requested_resolution.y) / height;
-	}
-
-	texture->SetScale(scale_factor);
 }
 
 bool GSTextureCache::ShallSearchTextureInsideRt()