diff --git a/src/swrenderer/drawers/r_draw.cpp b/src/swrenderer/drawers/r_draw.cpp
index d7a6ddd410..8db9d3be8d 100644
--- a/src/swrenderer/drawers/r_draw.cpp
+++ b/src/swrenderer/drawers/r_draw.cpp
@@ -225,6 +225,7 @@ namespace swrenderer
 			if (rendertarget->IsBgra())
 			{
 				uint32_t *destorg = (uint32_t*)rendertarget->GetBuffer();
+				destorg += viewwindowx + viewwindowy * rendertarget->GetPitch();
 				uint32_t *dest = (uint32_t*)args.Dest();
 				int offset  = (int)(ptrdiff_t)(dest - destorg);
 				x = offset % rendertarget->GetPitch();
@@ -233,6 +234,7 @@ namespace swrenderer
 			else
 			{
 				uint8_t *destorg = rendertarget->GetBuffer();
+				destorg += viewwindowx + viewwindowy * rendertarget->GetPitch();
 				uint8_t *dest = (uint8_t*)args.Dest();
 				int offset = (int)(ptrdiff_t)(dest - destorg);
 				x = offset % rendertarget->GetPitch();
@@ -247,6 +249,7 @@ namespace swrenderer
 			if (rendertarget->IsBgra())
 			{
 				uint32_t *destorg = (uint32_t*)rendertarget->GetBuffer();
+				destorg += viewwindowx + viewwindowy * rendertarget->GetPitch();
 				uint32_t *dest = (uint32_t*)args.Dest();
 				int offset = (int)(ptrdiff_t)(dest - destorg);
 				x = offset % rendertarget->GetPitch();
@@ -255,6 +258,7 @@ namespace swrenderer
 			else
 			{
 				uint8_t *destorg = rendertarget->GetBuffer();
+				destorg += viewwindowx + viewwindowy * rendertarget->GetPitch();
 				uint8_t *dest = (uint8_t*)args.Dest();
 				int offset = (int)(ptrdiff_t)(dest - destorg);
 				x = offset % rendertarget->GetPitch();
diff --git a/src/swrenderer/plane/r_flatplane.cpp b/src/swrenderer/plane/r_flatplane.cpp
index d582aaf48c..8d01205599 100644
--- a/src/swrenderer/plane/r_flatplane.cpp
+++ b/src/swrenderer/plane/r_flatplane.cpp
@@ -178,7 +178,8 @@ namespace swrenderer
 		double curyfrac = baseyfrac + ystepscale * (x1 - minx);
 
 		double distance = viewport->PlaneDepth(y, planeheight);
-		float zbufferdepth = 1.0f / (distance * Thread->Viewport->viewwindow.FocalTangent);
+
+		float zbufferdepth = (float)(1.0 / fabs(planeheight / Thread->Viewport->ScreenToViewY(y, 1.0)));
 
 		drawerargs.SetTextureUStep(distance * xstepscale / drawerargs.TextureWidth());
 		drawerargs.SetTextureUPos((distance * curxfrac + pviewx) / drawerargs.TextureWidth());