diff --git a/src/polyrenderer/scene/poly_sky.cpp b/src/polyrenderer/scene/poly_sky.cpp
index 2f4bc5f8c..c30dca34e 100644
--- a/src/polyrenderer/scene/poly_sky.cpp
+++ b/src/polyrenderer/scene/poly_sky.cpp
@@ -37,31 +37,32 @@ PolySkyDome::PolySkyDome()
 
 void PolySkyDome::Render(const TriMatrix &worldToClip)
 {
+#ifdef USE_GL_DOME_MATH
+	TriMatrix modelMatrix = GLSkyMath();
+#else
+	TriMatrix modelMatrix = TriMatrix::identity();
+
 	PolySkySetup frameSetup;
 	frameSetup.Update();
 
 	if (frameSetup != mCurrentSetup)
 	{
-		double frontTexWidth = (double)frameSetup.frontskytex->GetWidth();
-		float scaleFrontU = (float)(frameSetup.frontcyl / frontTexWidth);
-		if (frameSetup.skyflip)
-			scaleFrontU = -scaleFrontU;
+		// frontcyl = pixels for full 360 degrees, front texture
+		// backcyl = pixels for full 360 degrees, back texture
+		// skymid = Y scaled pixel offset
+		// sky1pos = unscaled X offset, front
+		// sky2pos = unscaled X offset, back
+		// frontpos = scaled X pixel offset (fixed point)
+		// backpos = scaled X pixel offset (fixed point)
+		// skyflip = flip X direction
 
-		float baseOffset = (float)(frameSetup.skyangle / 65536.0 / frontTexWidth);
-		float offsetFrontU = baseOffset * scaleFrontU + (float)(frameSetup.frontpos / 65536.0 / frontTexWidth);
+		float scaleBaseV = 1.42f;
+		float offsetBaseV = 0.25f;
 
-		float scaleFrontV = (float)(frameSetup.frontskytex->Scale.Y * 1.6);
-		float offsetFrontV;
-
-		// BTSX
-		/*{
-			offsetFrontU += 0.5f;
-			offsetFrontV = (float)((28.0f - frameSetup.skymid) / frameSetup.frontskytex->GetHeight());
-		}*/
-		// E1M1
-		{
-			offsetFrontV = (float)((28.0f + frameSetup.skymid) / frameSetup.frontskytex->GetHeight());
-		}
+		float scaleFrontU = frameSetup.frontcyl / (float)frameSetup.frontskytex->GetWidth();
+		float scaleFrontV = (float)frameSetup.frontskytex->Scale.Y * scaleBaseV;
+		float offsetFrontU = (float)(frameSetup.frontpos / 65536.0 / frameSetup.frontskytex->GetWidth());
+		float offsetFrontV = (float)((frameSetup.skymid / frameSetup.frontskytex->GetHeight() + offsetBaseV) * scaleBaseV);
 
 		unsigned int count = mVertices.Size();
 		for (unsigned int i = 0; i < count; i++)
@@ -72,9 +73,10 @@ void PolySkyDome::Render(const TriMatrix &worldToClip)
 
 		mCurrentSetup = frameSetup;
 	}
+#endif
 
 	const auto &viewpoint = PolyRenderer::Instance()->Viewpoint;
-	TriMatrix objectToWorld = TriMatrix::translate((float)viewpoint.Pos.X, (float)viewpoint.Pos.Y, (float)viewpoint.Pos.Z);
+	TriMatrix objectToWorld = TriMatrix::translate((float)viewpoint.Pos.X, (float)viewpoint.Pos.Y, (float)viewpoint.Pos.Z) * modelMatrix;
 	objectToClip = worldToClip * objectToWorld;
 
 	int rc = mRows + 1;
@@ -203,6 +205,80 @@ void PolySkyDome::SkyVertex(int r, int c, bool zflip)
 	mInitialUV.Push({ vert.u, vert.v });
 }
 
+TriMatrix PolySkyDome::GLSkyMath()
+{
+	PolySkySetup frameSetup;
+	frameSetup.Update();
+	mCurrentSetup = frameSetup;
+
+	float x_offset = 0.0f;
+	float y_offset = 0.0f;
+	bool mirror = false;
+	FTexture *tex = mCurrentSetup.frontskytex;
+	float skyoffset = 0.0f; // skyoffset debugging CVAR in GL renderer
+
+	int texh = 0;
+	int texw = 0;
+
+	// 57 world units roughly represent one sky texel for the glTranslate call.
+	const float skyoffsetfactor = 57;
+
+	TriMatrix modelMatrix = TriMatrix::identity();
+	if (tex)
+	{
+		texw = tex->GetWidth();
+		texh = tex->GetHeight();
+
+		modelMatrix = TriMatrix::rotate(-180.0f + x_offset, 0.f, 0.f, 1.f);
+
+		float xscale = texw < 1024.f ? floor(1024.f / float(texw)) : 1.f;
+		float yscale = 1.f;
+		if (texh <= 128 && (level.flags & LEVEL_FORCETILEDSKY))
+		{
+			modelMatrix = modelMatrix * TriMatrix::translate(0.f, 0.f, (-40 + tex->SkyOffset + skyoffset)*skyoffsetfactor);
+			modelMatrix = modelMatrix * TriMatrix::scale(1.f, 1.f, 1.2f * 1.17f);
+			yscale = 240.f / texh;
+		}
+		else if (texh < 128)
+		{
+			// smaller sky textures must be tiled. We restrict it to 128 sky pixels, though
+			modelMatrix = modelMatrix * TriMatrix::translate(0.f, 0.f, -1250.f);
+			modelMatrix = modelMatrix * TriMatrix::scale(1.f, 1.f, 128 / 230.f);
+			yscale = (float)(128 / texh); // intentionally left as integer.
+		}
+		else if (texh < 200)
+		{
+			modelMatrix = modelMatrix * TriMatrix::translate(0.f, 0.f, -1250.f);
+			modelMatrix = modelMatrix * TriMatrix::scale(1.f, 1.f, texh / 230.f);
+		}
+		else if (texh <= 240)
+		{
+			modelMatrix = modelMatrix * TriMatrix::translate(0.f, 0.f, (200 - texh + tex->SkyOffset + skyoffset)*skyoffsetfactor);
+			modelMatrix = modelMatrix * TriMatrix::scale(1.f, 1.f, 1.f + ((texh - 200.f) / 200.f) * 1.17f);
+		}
+		else
+		{
+			modelMatrix = modelMatrix * TriMatrix::translate(0.f, 0.f, (-40 + tex->SkyOffset + skyoffset)*skyoffsetfactor);
+			modelMatrix = modelMatrix * TriMatrix::scale(1.f, 1.f, 1.2f * 1.17f);
+			yscale = 240.f / texh;
+		}
+
+		float offsetU = 1.0f;
+		float offsetV = y_offset / texh;
+		float scaleU = mirror ? -xscale : xscale;
+		float scaleV = yscale;
+
+		unsigned int count = mVertices.Size();
+		for (unsigned int i = 0; i < count; i++)
+		{
+			mVertices[i].u = offsetU + mInitialUV[i].X * scaleU;
+			mVertices[i].v = offsetV + mInitialUV[i].Y * scaleV;
+		}
+	}
+
+	return modelMatrix;
+}
+
 /////////////////////////////////////////////////////////////////////////////
 
 void PolySkySetup::Update()
@@ -291,10 +367,6 @@ void PolySkySetup::Update()
 
 		int frontxscale = int(frontskytex->Scale.X * 1024);
 		frontcyl = MAX(frontskytex->GetWidth(), frontxscale);
-		if (skystretch)
-		{
-			skymid = skymid * frontskytex->GetScaledHeightDouble() / SKYSTRETCH_HEIGHT;
-		}
 	}
 
 	frontpos = int(fmod(frontdpos, sky1cyl * 65536.0));
diff --git a/src/polyrenderer/scene/poly_sky.h b/src/polyrenderer/scene/poly_sky.h
index bf8f7e202..4fc30da70 100644
--- a/src/polyrenderer/scene/poly_sky.h
+++ b/src/polyrenderer/scene/poly_sky.h
@@ -63,5 +63,7 @@ private:
 
 	TriVertex SetVertexXYZ(float xx, float yy, float zz, float uu = 0, float vv = 0);
 
+	TriMatrix GLSkyMath();
+
 	PolySkySetup mCurrentSetup;
 };