Viewport: Reduce unnecessary region redraws when scrolling viewports

src/blitter/32bpp_anim.cpp

@@ -509,7 +509,7 @@ void Blitter_32bppAnim::CopyToBuffer(const void *video, void *dst, int width, in
 	}
 }
 
-void Blitter_32bppAnim::ScrollBuffer(void *video, int &left, int &top, int &width, int &height, int scroll_x, int scroll_y)
+void Blitter_32bppAnim::ScrollBuffer(void *video, int left, int top, int width, int height, int scroll_x, int scroll_y)
 {
 	assert(!_screen_disable_anim);
 	assert(video >= _screen.dst_ptr && video <= (uint32 *)_screen.dst_ptr + _screen.width + _screen.height * _screen.pitch);

src/blitter/32bpp_anim.hpp

@@ -44,7 +44,7 @@ public:
 	void DrawRect(void *video, int width, int height, uint8 colour) override;
 	void CopyFromBuffer(void *video, const void *src, int width, int height) override;
 	void CopyToBuffer(const void *video, void *dst, int width, int height) override;
-	void ScrollBuffer(void *video, int &left, int &top, int &width, int &height, int scroll_x, int scroll_y) override;
+	void ScrollBuffer(void *video, int left, int top, int width, int height, int scroll_x, int scroll_y) override;
 	int BufferSize(int width, int height) override;
 	void PaletteAnimate(const Palette &palette) override;
 	Blitter::PaletteAnimation UsePaletteAnimation() override;

src/blitter/32bpp_base.cpp

@@ -101,7 +101,7 @@ void Blitter_32bppBase::CopyImageToBuffer(const void *video, void *dst, int widt
 	}
 }
 
-void Blitter_32bppBase::ScrollBuffer(void *video, int &left, int &top, int &width, int &height, int scroll_x, int scroll_y)
+void Blitter_32bppBase::ScrollBuffer(void *video, int left, int top, int width, int height, int scroll_x, int scroll_y)
 {
 	const uint32 *src;
 	uint32 *dst;

src/blitter/32bpp_base.hpp

@@ -28,7 +28,7 @@ public:
 	void CopyFromBuffer(void *video, const void *src, int width, int height) override;
 	void CopyToBuffer(const void *video, void *dst, int width, int height) override;
 	void CopyImageToBuffer(const void *video, void *dst, int width, int height, int dst_pitch) override;
-	void ScrollBuffer(void *video, int &left, int &top, int &width, int &height, int scroll_x, int scroll_y) override;
+	void ScrollBuffer(void *video, int left, int top, int width, int height, int scroll_x, int scroll_y) override;
 	int BufferSize(int width, int height) override;
 	void PaletteAnimate(const Palette &palette) override;
 	Blitter::PaletteAnimation UsePaletteAnimation() override;

src/blitter/8bpp_base.cpp

@@ -90,7 +90,7 @@ void Blitter_8bppBase::CopyImageToBuffer(const void *video, void *dst, int width
 	}
 }
 
-void Blitter_8bppBase::ScrollBuffer(void *video, int &left, int &top, int &width, int &height, int scroll_x, int scroll_y)
+void Blitter_8bppBase::ScrollBuffer(void *video, int left, int top, int width, int height, int scroll_x, int scroll_y)
 {
 	const uint8 *src;
 	uint8 *dst;

src/blitter/8bpp_base.hpp

@@ -25,7 +25,7 @@ public:
 	void CopyFromBuffer(void *video, const void *src, int width, int height) override;
 	void CopyToBuffer(const void *video, void *dst, int width, int height) override;
 	void CopyImageToBuffer(const void *video, void *dst, int width, int height, int dst_pitch) override;
-	void ScrollBuffer(void *video, int &left, int &top, int &width, int &height, int scroll_x, int scroll_y) override;
+	void ScrollBuffer(void *video, int left, int top, int width, int height, int scroll_x, int scroll_y) override;
 	int BufferSize(int width, int height) override;
 	void PaletteAnimate(const Palette &palette) override;
 	Blitter::PaletteAnimation UsePaletteAnimation() override;

src/blitter/base.hpp

@@ -198,7 +198,7 @@ public:
 	 * @param scroll_x How much to scroll in X.
 	 * @param scroll_y How much to scroll in Y.
 	 */
-	virtual void ScrollBuffer(void *video, int &left, int &top, int &width, int &height, int scroll_x, int scroll_y) = 0;
+	virtual void ScrollBuffer(void *video, int left, int top, int width, int height, int scroll_x, int scroll_y) = 0;
 
 	/**
 	 * Calculate how much memory there is needed for an image of this size in the video-buffer.

src/blitter/null.hpp

@@ -28,7 +28,7 @@ public:
 	void CopyFromBuffer(void *video, const void *src, int width, int height) override {};
 	void CopyToBuffer(const void *video, void *dst, int width, int height) override {};
 	void CopyImageToBuffer(const void *video, void *dst, int width, int height, int dst_pitch) override {};
-	void ScrollBuffer(void *video, int &left, int &top, int &width, int &height, int scroll_x, int scroll_y) override {};
+	void ScrollBuffer(void *video, int left, int top, int width, int height, int scroll_x, int scroll_y) override {};
 	int BufferSize(int width, int height) override { return 0; };
 	void PaletteAnimate(const Palette &palette) override { };
 	Blitter::PaletteAnimation UsePaletteAnimation() override { return Blitter::PALETTE_ANIMATION_NONE; };

src/gfx.cpp

@@ -79,21 +79,6 @@ static uint _dirty_bytes_per_line = 0;
 static byte *_dirty_blocks = nullptr;
 extern uint _dirty_block_colour;
 
-void GfxScroll(int left, int top, int width, int height, int xo, int yo)
-{
-	Blitter *blitter = BlitterFactory::GetCurrentBlitter();
-
-	if (xo == 0 && yo == 0) return;
-
-	if (_cursor.visible) UndrawMouseCursor();
-
-	if (_networking) NetworkUndrawChatMessage();
-
-	blitter->ScrollBuffer(_screen.dst_ptr, left, top, width, height, xo, yo);
-	/* This part of the screen is now dirty. */
-	VideoDriver::GetInstance()->MakeDirty(left, top, width, height);
-}
-
 
 /**
  * Applies a certain FillRectMode-operation to a rectangle [left, right] x [top, bottom] on the screen.

src/gfx_func.h

@@ -86,7 +86,6 @@ void UndrawMouseCursor();
 static const int DRAW_STRING_BUFFER = 2048;
 
 void RedrawScreenRect(int left, int top, int right, int bottom);
-void GfxScroll(int left, int top, int width, int height, int xo, int yo);
 
 Dimension GetSpriteSize(SpriteID sprid, Point *offset = nullptr, ZoomLevel zoom = ZOOM_LVL_GUI);
 void DrawSpriteViewport(SpriteID img, PaletteID pal, int x, int y, const SubSprite *sub = nullptr);

src/viewport.cpp

@@ -105,6 +105,7 @@
 #include "gui.h"
 #include "core/container_func.hpp"
 #include "tunnelbridge_map.h"
+#include "video/video_driver.hpp"
 
 #include <map>
 #include <vector>
@@ -391,9 +392,15 @@ void InitializeWindowViewport(Window *w, int x, int y,
 
 static Point _vp_move_offs;
 
-static void DoSetViewportPosition(const Window *w, int left, int top, int width, int height)
+struct ViewportRedrawRegion {
+	Rect coords;
+};
+
+static std::vector<ViewportRedrawRegion> _vp_redraw_regions;
+
+static void DoViewportRedrawRegions(const Window *w, int left, int top, int width, int height)
 {
-	IncrementWindowUpdateNumber();
+	if (width <= 0 || height <= 0) return;
 
 	FOR_ALL_WINDOWS_FROM_BACK_FROM(w, w) {
 		if (left + width > w->left &&
@@ -402,26 +409,26 @@ static void DoSetViewportPosition(const Window *w, int left, int top, int width,
 				w->top + w->height > top) {
 
 			if (left < w->left) {
-				DoSetViewportPosition(w, left, top, w->left - left, height);
+				DoViewportRedrawRegions(w, left, top, w->left - left, height);
-				DoSetViewportPosition(w, left + (w->left - left), top, width - (w->left - left), height);
+				DoViewportRedrawRegions(w, left + (w->left - left), top, width - (w->left - left), height);
 				return;
 			}
 
 			if (left + width > w->left + w->width) {
-				DoSetViewportPosition(w, left, top, (w->left + w->width - left), height);
+				DoViewportRedrawRegions(w, left, top, (w->left + w->width - left), height);
-				DoSetViewportPosition(w, left + (w->left + w->width - left), top, width - (w->left + w->width - left), height);
+				DoViewportRedrawRegions(w, left + (w->left + w->width - left), top, width - (w->left + w->width - left), height);
 				return;
 			}
 
 			if (top < w->top) {
-				DoSetViewportPosition(w, left, top, width, (w->top - top));
+				DoViewportRedrawRegions(w, left, top, width, (w->top - top));
-				DoSetViewportPosition(w, left, top + (w->top - top), width, height - (w->top - top));
+				DoViewportRedrawRegions(w, left, top + (w->top - top), width, height - (w->top - top));
 				return;
 			}
 
 			if (top + height > w->top + w->height) {
-				DoSetViewportPosition(w, left, top, width, (w->top + w->height - top));
+				DoViewportRedrawRegions(w, left, top, width, (w->top + w->height - top));
-				DoSetViewportPosition(w, left, top + (w->top + w->height - top), width, height - (w->top + w->height - top));
+				DoViewportRedrawRegions(w, left, top + (w->top + w->height - top), width, height - (w->top + w->height - top));
 				return;
 			}
 
@@ -429,31 +436,132 @@ static void DoSetViewportPosition(const Window *w, int left, int top, int width,
 		}
 	}
 
+	_vp_redraw_regions.push_back({ { left, top, left + width, top + height } });
+}
+
+static void DoSetViewportPositionFillRegion(int left, int top, int width, int height, int xo, int yo) {
+	int src_left = left - xo;
+	int src_top = top - yo;
+	int src_right = src_left + width;
+	int src_bottom = src_top + height;
+	for (const auto &region : _vp_redraw_regions) {
+		if (region.coords.left < src_right &&
+				region.coords.right > src_left &&
+				region.coords.top < src_bottom &&
+				region.coords.bottom > src_top) {
+			/* can use this region as a source */
+			if (src_left < region.coords.left) {
+				DoSetViewportPositionFillRegion(src_left + xo, src_top + yo, region.coords.left - src_left, height, xo, yo);
+				src_left = region.coords.left;
+				width = src_right - src_left;
+			}
+			if (src_top < region.coords.top) {
+				DoSetViewportPositionFillRegion(src_left + xo, src_top + yo, width, region.coords.top - src_top, xo, yo);
+				src_top = region.coords.top;
+				height = src_bottom - src_top;
+			}
+			if (src_right > region.coords.right) {
+				DoSetViewportPositionFillRegion(region.coords.right + xo, src_top + yo, src_right - region.coords.right, height, xo, yo);
+				src_right = region.coords.right;
+				width = src_right - src_left;
+			}
+			if (src_bottom > region.coords.bottom) {
+				DoSetViewportPositionFillRegion(src_left + xo, region.coords.bottom + yo, width, src_bottom - region.coords.bottom, xo, yo);
+				src_bottom = region.coords.bottom;
+				height = src_bottom - src_top;
+			}
+
+			if (xo >= 0) {
+				/* scrolling left, moving pixels right */
+				width += xo;
+			} else {
+				/* scrolling right, moving pixels left */
+				src_left += xo;
+				width -= xo;
+			}
+			if (yo >= 0) {
+				/* scrolling down, moving pixels up */
+				height += yo;
+			} else {
+				/* scrolling up, moving pixels down */
+				src_top += yo;
+				height -= yo;
+			}
+			BlitterFactory::GetCurrentBlitter()->ScrollBuffer(_screen.dst_ptr, src_left, src_top, width, height, xo, yo);
+
+			return;
+		}
+	}
+	DrawOverlappedWindowForAll(left, top, left + width, top + height);
+};
+
+static void DoSetViewportPosition(const Window *w, const int left, const int top, const int width, const int height)
 {
-		int xo = _vp_move_offs.x;
+	const int xo = _vp_move_offs.x;
-		int yo = _vp_move_offs.y;
+	const int yo = _vp_move_offs.y;
+	if (xo == 0 && yo == 0) return;
+
+
+	IncrementWindowUpdateNumber();
+
+	_vp_redraw_regions.clear();
+	DoViewportRedrawRegions(w, left, top, width, height);
 
 	if (abs(xo) >= width || abs(yo) >= height) {
-			/* fully_outside */
+		/* fully outside */
-			RedrawScreenRect(left, top, left + width, top + height);
+		for (ViewportRedrawRegion &vrr : _vp_redraw_regions) {
+			RedrawScreenRect(vrr.coords.left, vrr.coords.top, vrr.coords.right, vrr.coords.bottom);
+		}
 		return;
 	}
 
-		GfxScroll(left, top, width, height, xo, yo);
+	Blitter *blitter = BlitterFactory::GetCurrentBlitter();
 
-		if (xo > 0) {
+	if (_cursor.visible) UndrawMouseCursor();
-			RedrawScreenRect(left, top, xo + left, top + height);
+
-			left += xo;
+	if (_networking) NetworkUndrawChatMessage();
-			width -= xo;
+
-		} else if (xo < 0) {
+	std::sort(_vp_redraw_regions.begin(), _vp_redraw_regions.end(), [&](const ViewportRedrawRegion &a, const ViewportRedrawRegion &b) {
-			RedrawScreenRect(left + width + xo, top, left + width, top + height);
+		if (a.coords.right <= b.coords.left) return xo > 0;
-			width += xo;
+		if (a.coords.left >= b.coords.right) return xo < 0;
+		if (a.coords.bottom <= b.coords.top) return yo > 0;
+		if (a.coords.top >= b.coords.bottom) return yo < 0;
+		NOT_REACHED();
+	});
+
+	while (!_vp_redraw_regions.empty()) {
+		const Rect &rect = _vp_redraw_regions.back().coords;
+		int left = rect.left;
+		int top = rect.top;
+		int width = rect.right - rect.left;
+		int height = rect.bottom - rect.top;
+		_vp_redraw_regions.pop_back();
+		VideoDriver::GetInstance()->MakeDirty(left, top, width, height);
+		int fill_width = abs(xo);
+		int fill_height = abs(yo);
+		if (fill_width < width && fill_height < height) {
+			blitter->ScrollBuffer(_screen.dst_ptr, left, top, width, height, xo, yo);
+		} else {
+			if (width < fill_width) fill_width = width;
+			if (height < fill_height) fill_height = height;
 		}
-
+		if (xo < 0) {
-		if (yo > 0) {
+			/* scrolling right, moving pixels left, fill in on right */
-			RedrawScreenRect(left, top, width + left, top + yo);
+			width -= fill_width;
-		} else if (yo < 0) {
+			DoSetViewportPositionFillRegion(left + width, top, fill_width, height, xo, yo);
-			RedrawScreenRect(left, top + height + yo, width + left, top + height);
+		} else if (xo > 0) {
+			/* scrolling left, moving pixels right, fill in on left */
+			DoSetViewportPositionFillRegion(left, top, fill_width, height, xo, yo);
+			width -= fill_width;
+			left += fill_width;
+		}
+		if (yo < 0 && width > 0) {
+			/* scrolling down, moving pixels up, fill in at bottom */
+			height -= fill_height;
+			DoSetViewportPositionFillRegion(left, top + height, width, fill_height, xo, yo);
+		} else if (yo > 0 && width > 0) {
+			/* scrolling up, moving pixels down, fill in at top */
+			DoSetViewportPositionFillRegion(left, top, width, fill_height, xo, yo);
 		}
 	}
 }