Codechange: Add InverseRemapCoords2 function for remapping viewport coordinates to underlying tile coordinates (Patch by adf88, #6583)

4 files changed, 72 insertions, 56 deletions

diff --git a/src/landscape.cpp b/src/landscape.cpp
index 18f27807d..eb1e404f0 100644
--- a/src/landscape.cpp
+++ b/src/landscape.cpp
@@ -90,6 +90,57 @@ extern const byte _slope_to_sprite_offset[32] = {
 static SnowLine *_snow_line = NULL;
 
 /**
+ * Map 2D viewport or smallmap coordinate to 3D world or tile coordinate.
+ * Function takes into account height of tiles and foundations.
+ *
+ * @param x X viewport 2D coordinate.
+ * @param y Y viewport 2D coordinate.
+ * @param clamp_to_map Clamp the coordinate outside of the map to the closest, non-void tile within the map.
+ * @return 3D world coordinate of point visible at the given screen coordinate (3D perspective).
+ *
+ * @note Inverse of #RemapCoords2 function. Smaller values may get rounded.
+ * @see InverseRemapCoords
+ */
+Point InverseRemapCoords2(int x, int y, bool clamp_to_map)
+{
+	/* Initial x/y world coordinate is like if the landscape
+	 * was completely flat on height 0. */
+	Point pt = InverseRemapCoords(x, y);
+
+	const uint min_coord = _settings_game.construction.freeform_edges ? TILE_SIZE : 0;
+	const uint max_x = MapMaxX() * TILE_SIZE - 1;
+	const uint max_y = MapMaxY() * TILE_SIZE - 1;
+
+	if (clamp_to_map) {
+		/* Bring the coordinates near to a valid range. At the top we allow a number
+		 * of extra tiles. This is mostly due to the tiles on the north side of
+		 * the map possibly being drawn higher due to the extra height levels. */
+		int extra_tiles = CeilDiv(_settings_game.construction.max_heightlevel * TILE_HEIGHT, TILE_PIXELS);
+		pt.x = Clamp(pt.x, -extra_tiles * TILE_SIZE, max_x);
+		pt.y = Clamp(pt.y, -extra_tiles * TILE_SIZE, max_y);
+	}
+
+	/* Now find the Z-world coordinate by fix point iteration.
+	 * This is a bit tricky because the tile height is non-continuous at foundations.
+	 * The clicked point should be approached from the back, otherwise there are regions that are not clickable.
+	 * (FOUNDATION_HALFTILE_LOWER on SLOPE_STEEP_S hides north halftile completely)
+	 * So give it a z-malus of 4 in the first iterations. */
+	int z = 0;
+	for (int i = 0; i < 5; i++) z = GetSlopePixelZ(Clamp(pt.x + max(z, 4) - 4, min_coord, max_x), Clamp(pt.y + max(z, 4) - 4, min_coord, max_y)) / 2;
+	for (int m = 3; m > 0; m--) z = GetSlopePixelZ(Clamp(pt.x + max(z, m) - m, min_coord, max_x), Clamp(pt.y + max(z, m) - m, min_coord, max_y)) / 2;
+	for (int i = 0; i < 5; i++) z = GetSlopePixelZ(Clamp(pt.x + z,             min_coord, max_x), Clamp(pt.y + z,             min_coord, max_y)) / 2;
+
+	pt.x += z;
+	pt.y += z;
+	if (clamp_to_map) {
+		pt.x = Clamp(pt.x, min_coord, max_x);
+		pt.y = Clamp(pt.y, min_coord, max_y);
+	}
+
+	return pt;
+}
+
+/**
  * Applies a foundation to a slope.
  *
  * @pre      Foundation and slope must be valid combined.
diff --git a/src/landscape.h b/src/landscape.h
index cb08d9d9e..cf366e09c 100644
--- a/src/landscape.h
+++ b/src/landscape.h
@@ -108,6 +108,7 @@ static inline Point RemapCoords2(int x, int y)
  * @param y Y coordinate of the 2D coordinate.
  * @return X and Y components of equivalent world or tile coordinate.
  * @note Inverse of #RemapCoords function. Smaller values may get rounded.
+ * @see InverseRemapCoords2
  */
 static inline Point InverseRemapCoords(int x, int y)
 {
@@ -115,6 +116,8 @@ static inline Point InverseRemapCoords(int x, int y)
 	return pt;
 }
 
+Point InverseRemapCoords2(int x, int y, bool clamp_to_map = false);
+
 uint ApplyFoundationToSlope(Foundation f, Slope *s);
 /**
  * Applies a foundation to a slope.
diff --git a/src/smallmap_gui.cpp b/src/smallmap_gui.cpp
index df9fd2df2..10eeca5d3 100644
--- a/src/smallmap_gui.cpp
+++ b/src/smallmap_gui.cpp
@@ -923,8 +923,8 @@ void SmallMapWindow::DrawMapIndicators() const
 	/* Find main viewport. */
 	const ViewPort *vp = FindWindowById(WC_MAIN_WINDOW, 0)->viewport;
 
-	Point upper_left_smallmap_coord  = TranslateXYToTileCoord(vp, vp->left, vp->top, false);
-	Point lower_right_smallmap_coord = TranslateXYToTileCoord(vp, vp->left + vp->width - 1, vp->top + vp->height - 1, false);
+	Point upper_left_smallmap_coord  = InverseRemapCoords2(vp->virtual_left, vp->virtual_top);
+	Point lower_right_smallmap_coord = InverseRemapCoords2(vp->virtual_left + vp->virtual_width - 1, vp->virtual_top + vp->virtual_height - 1);
 
 	Point upper_left = this->RemapTile(upper_left_smallmap_coord.x / (int)TILE_SIZE, upper_left_smallmap_coord.y / (int)TILE_SIZE);
 	upper_left.x -= this->subscroll;
@@ -1645,7 +1645,7 @@ void SmallMapWindow::SetNewScroll(int sx, int sy, int sub)
 void SmallMapWindow::SmallMapCenterOnCurrentPos()
 {
 	const ViewPort *vp = FindWindowById(WC_MAIN_WINDOW, 0)->viewport;
-	Point viewport_center = TranslateXYToTileCoord(vp, vp->left + vp->width / 2, vp->top + vp->height / 2);
+	Point viewport_center = InverseRemapCoords2(vp->virtual_left + vp->virtual_width / 2, vp->virtual_top + vp->virtual_height / 2);
 
 	int sub;
 	const NWidgetBase *wid = this->GetWidget<NWidgetBase>(WID_SM_MAP);
diff --git a/src/viewport.cpp b/src/viewport.cpp
index 5e72aaa23..da1085161 100644
--- a/src/viewport.cpp
+++ b/src/viewport.cpp
@@ -399,65 +399,27 @@ ViewPort *IsPtInWindowViewport(const Window *w, int x, int y)
 }
 
 /**
- * Translate screen coordinate in a viewport to a tile coordinate
+ * Translate screen coordinate in a viewport to underlying tile coordinate.
+ *
+ * Returns exact point of the map that is visible in the given place
+ * of the viewport (3D perspective), height of tiles and foundations matter.
+ *
  * @param vp  Viewport that contains the (\a x, \a y) screen coordinate
- * @param x   Screen x coordinate
- * @param y   Screen y coordinate
- * @param clamp_to_map Clamp the coordinate outside of the map to the closest tile within the map.
- * @return Tile coordinate
+ * @param x   Screen x coordinate, distance in pixels from the left edge of viewport frame
+ * @param y   Screen y coordinate, distance in pixels from the top edge of viewport frame
+ * @param clamp_to_map Clamp the coordinate outside of the map to the closest, non-void tile within the map
+ * @return Tile coordinate or (-1, -1) if given x or y is not within viewport frame
  */
 Point TranslateXYToTileCoord(const ViewPort *vp, int x, int y, bool clamp_to_map)
 {
-	Point pt;
-	int a, b;
-	int z;
-
-	if ( (uint)(x -= vp->left) >= (uint)vp->width ||
-				(uint)(y -= vp->top) >= (uint)vp->height) {
-				Point pt = {-1, -1};
-				return pt;
-	}
-
-	x = (ScaleByZoom(x, vp->zoom) + vp->virtual_left) >> (2 + ZOOM_LVL_SHIFT);
-	y = (ScaleByZoom(y, vp->zoom) + vp->virtual_top) >> (1 + ZOOM_LVL_SHIFT);
-
-	a = y - x;
-	b = y + x;
-
-	if (clamp_to_map) {
-		/* Bring the coordinates near to a valid range. This is mostly due to the
-		 * tiles on the north side of the map possibly being drawn too high due to
-		 * the extra height levels. So at the top we allow a number of extra tiles.
-		 * This number is based on the tile height and pixels. */
-		int extra_tiles = CeilDiv(_settings_game.construction.max_heightlevel * TILE_HEIGHT, TILE_PIXELS);
-		a = Clamp(a, -extra_tiles * TILE_SIZE, MapMaxX() * TILE_SIZE - 1);
-		b = Clamp(b, -extra_tiles * TILE_SIZE, MapMaxY() * TILE_SIZE - 1);
+	if (!IsInsideBS(x, vp->left, vp->width) || !IsInsideBS(y, vp->top, vp->height)) {
+		Point pt = { -1, -1 };
+		return pt;
 	}
 
-	/* (a, b) is the X/Y-world coordinate that belongs to (x,y) if the landscape would be completely flat on height 0.
-	 * Now find the Z-world coordinate by fix point iteration.
-	 * This is a bit tricky because the tile height is non-continuous at foundations.
-	 * The clicked point should be approached from the back, otherwise there are regions that are not clickable.
-	 * (FOUNDATION_HALFTILE_LOWER on SLOPE_STEEP_S hides north halftile completely)
-	 * So give it a z-malus of 4 in the first iterations.
-	 */
-	z = 0;
-
-	int min_coord = _settings_game.construction.freeform_edges ? TILE_SIZE : 0;
-
-	for (int i = 0; i < 5; i++) z = GetSlopePixelZ(Clamp(a + max(z, 4) - 4, min_coord, MapMaxX() * TILE_SIZE - 1), Clamp(b + max(z, 4) - 4, min_coord, MapMaxY() * TILE_SIZE - 1)) / 2;
-	for (int malus = 3; malus > 0; malus--) z = GetSlopePixelZ(Clamp(a + max(z, malus) - malus, min_coord, MapMaxX() * TILE_SIZE - 1), Clamp(b + max(z, malus) - malus, min_coord, MapMaxY() * TILE_SIZE - 1)) / 2;
-	for (int i = 0; i < 5; i++) z = GetSlopePixelZ(Clamp(a + z, min_coord, MapMaxX() * TILE_SIZE - 1), Clamp(b + z, min_coord, MapMaxY() * TILE_SIZE - 1)) / 2;
-
-	if (clamp_to_map) {
-		pt.x = Clamp(a + z, min_coord, MapMaxX() * TILE_SIZE - 1);
-		pt.y = Clamp(b + z, min_coord, MapMaxY() * TILE_SIZE - 1);
-	} else {
-		pt.x = a + z;
-		pt.y = b + z;
-	}
-
-	return pt;
+	return InverseRemapCoords2(
+			ScaleByZoom(x - vp->left, vp->zoom) + vp->virtual_left,
+			ScaleByZoom(y - vp->top, vp->zoom) + vp->virtual_top, clamp_to_map);
 }
 
 /* When used for zooming, check area below current coordinates (x,y)