# HG changeset patch
# User michi_cc <michi_cc@openttd.org>
# Date 1328362153 0
# Node ID 35ff175e9a6eeef6329d5a77fc47c6b0b747e535
# Parent  1953cefd0c2be3b4256d00441133b952fdb55047
(svn r23889) -Codechange: Centralise sprite resizing in one place. (peter1138)

diff --git a/src/blitter/32bpp_optimized.cpp b/src/blitter/32bpp_optimized.cpp
--- a/src/blitter/32bpp_optimized.cpp
+++ b/src/blitter/32bpp_optimized.cpp
@@ -207,55 +207,6 @@
 	}
 }
 
-/**
- * Resizes the sprite in a very simple way, takes every n-th pixel and every n-th row
- *
- * @param sprite_src sprite to resize
- * @param zoom resizing scale
- * @return resized sprite
- */
-static const SpriteLoader::Sprite *ResizeSprite(const SpriteLoader::Sprite *sprite_src, ZoomLevel zoom)
-{
-	SpriteLoader::Sprite *sprite = MallocT<SpriteLoader::Sprite>(1);
-
-	if (zoom == ZOOM_LVL_NORMAL) {
-		memcpy(sprite, sprite_src, sizeof(*sprite));
-		uint size = sprite_src->height * sprite_src->width;
-		sprite->data = MallocT<SpriteLoader::CommonPixel>(size);
-		memcpy(sprite->data, sprite_src->data, size * sizeof(SpriteLoader::CommonPixel));
-		return sprite;
-	}
-
-	sprite->height = UnScaleByZoom(sprite_src->height, zoom);
-	sprite->width  = UnScaleByZoom(sprite_src->width,  zoom);
-	sprite->x_offs = UnScaleByZoom(sprite_src->x_offs, zoom);
-	sprite->y_offs = UnScaleByZoom(sprite_src->y_offs, zoom);
-
-	uint size = sprite->height * sprite->width;
-	SpriteLoader::CommonPixel *dst = sprite->data = CallocT<SpriteLoader::CommonPixel>(size);
-
-	const SpriteLoader::CommonPixel *src = (SpriteLoader::CommonPixel *)sprite_src->data;
-	const SpriteLoader::CommonPixel *src_end = src + sprite_src->height * sprite_src->width;
-
-	uint scaled_1 = ScaleByZoom(1, zoom);
-
-	for (uint y = 0; y < sprite->height; y++) {
-		if (src >= src_end) src = src_end - sprite_src->width;
-
-		const SpriteLoader::CommonPixel *src_ln = src + sprite_src->width * scaled_1;
-		for (uint x = 0; x < sprite->width; x++) {
-			if (src >= src_ln) src = src_ln - 1;
-			*dst = *src;
-			dst++;
-			src += scaled_1;
-		}
-
-		src = src_ln;
-	}
-
-	return sprite;
-}
-
 Sprite *Blitter_32bppOptimized::Encode(SpriteLoader::Sprite *sprite, AllocatorProc *allocator)
 {
 	/* streams of pixels (a, r, g, b channels)
@@ -287,7 +238,7 @@
 	}
 
 	for (ZoomLevel z = zoom_min; z <= zoom_max; z++) {
-		const SpriteLoader::Sprite *src_orig = ResizeSprite(sprite, z);
+		const SpriteLoader::Sprite *src_orig = &sprite[z];
 
 		uint size = src_orig->height * src_orig->width;
 
@@ -371,9 +322,6 @@
 
 		lengths[z][0] = (byte *)dst_px_ln - (byte *)dst_px_orig[z]; // all are aligned to 4B boundary
 		lengths[z][1] = (byte *)dst_n_ln  - (byte *)dst_n_orig[z];
-
-		free(src_orig->data);
-		free(src_orig);
 	}
 
 	uint len = 0; // total length of data
diff --git a/src/blitter/8bpp_optimized.cpp b/src/blitter/8bpp_optimized.cpp
--- a/src/blitter/8bpp_optimized.cpp
+++ b/src/blitter/8bpp_optimized.cpp
@@ -130,7 +130,7 @@
 	}
 
 	for (ZoomLevel i = zoom_min; i <= zoom_max; i++) {
-		memory += UnScaleByZoom(sprite->height, i) * UnScaleByZoom(sprite->width, i);
+		memory += sprite[i].width * sprite[i].height;
 	}
 
 	/* We have no idea how much memory we really need, so just guess something */
@@ -150,9 +150,8 @@
 		temp_dst->offset[i] = offset;
 
 		/* cache values, because compiler can't cache it */
-		int scaled_height = UnScaleByZoom(sprite->height, i);
-		int scaled_width  = UnScaleByZoom(sprite->width,  i);
-		int scaled_1      =   ScaleByZoom(1,              i);
+		int scaled_height = sprite[i].height;
+		int scaled_width  = sprite[i].width;
 
 		for (int y = 0; y < scaled_height; y++) {
 			uint trans = 0;
@@ -161,18 +160,10 @@
 			byte *count_dst = NULL;
 
 			/* Store the scaled image */
-			const SpriteLoader::CommonPixel *src = &sprite->data[ScaleByZoom(y, i) * sprite->width];
-			const SpriteLoader::CommonPixel *src_end = &src[sprite->width];
+			const SpriteLoader::CommonPixel *src = &sprite[i].data[y * sprite[i].width];
 
 			for (int x = 0; x < scaled_width; x++) {
-				uint colour = 0;
-
-				/* Get the colour keeping in mind the zoom-level */
-				for (int j = 0; j < scaled_1; j++) {
-					if (src->m != 0) colour = src->m;
-					/* Because of the scaling it might happen we read outside the buffer. Avoid that. */
-					if (++src == src_end) break;
-				}
+				uint colour = src++->m;
 
 				if (last_colour == 0 || colour == 0 || pixels == 255) {
 					if (count_dst != NULL) {
diff --git a/src/fontcache.cpp b/src/fontcache.cpp
--- a/src/fontcache.cpp
+++ b/src/fontcache.cpp
@@ -1152,7 +1152,7 @@
 	if (width > 256 || height > 256) usererror("Font glyph is too large");
 
 	/* FreeType has rendered the glyph, now we allocate a sprite and copy the image into it */
-	sprite.AllocateData(width * height);
+	sprite.AllocateData(ZOOM_LVL_NORMAL, width * height);
 	sprite.type = ST_FONT;
 	sprite.width = width;
 	sprite.height = height;
diff --git a/src/spritecache.cpp b/src/spritecache.cpp
--- a/src/spritecache.cpp
+++ b/src/spritecache.cpp
@@ -13,11 +13,14 @@
 #include "fileio_func.h"
 #include "spriteloader/grf.hpp"
 #include "gfx_func.h"
+#include "zoom_func.h"
+#include "settings_type.h"
 #ifdef WITH_PNG
 #include "spriteloader/png.hpp"
 #endif /* WITH_PNG */
 #include "blitter/factory.hpp"
 #include "core/math_func.hpp"
+#include "core/mem_func.hpp"
 
 #include "table/sprites.h"
 #include "table/palette_convert.h"
@@ -156,6 +159,177 @@
 	return _spritecache_items;
 }
 
+static bool ResizeSpriteIn(SpriteLoader::Sprite *sprite, ZoomLevel src, ZoomLevel tgt)
+{
+	uint8 scaled_1 = UnScaleByZoom(1, (ZoomLevel)(tgt - src));
+
+	/* Check for possible memory overflow. */
+	if (sprite[src].width * scaled_1 > UINT16_MAX || sprite[src].height * scaled_1 > UINT16_MAX) return false;
+
+	sprite[tgt].width  = sprite[src].width  * scaled_1;
+	sprite[tgt].height = sprite[src].height * scaled_1;
+	sprite[tgt].x_offs = sprite[src].x_offs * scaled_1;
+	sprite[tgt].y_offs = sprite[src].y_offs * scaled_1;
+
+	sprite[tgt].AllocateData(tgt, sprite[tgt].width * sprite[tgt].height);
+
+	SpriteLoader::CommonPixel *dst = sprite[tgt].data;
+	for (int y = 0; y < sprite[tgt].height; y++) {
+		const SpriteLoader::CommonPixel *src_ln = &sprite[src].data[y / scaled_1 * sprite[src].width];
+		for (int x = 0; x < sprite[tgt].width; x++) {
+			*dst = src_ln[x / scaled_1];
+			dst++;
+		}
+	}
+
+	return true;
+}
+
+static void ResizeSpriteOut(SpriteLoader::Sprite *sprite, ZoomLevel zoom)
+{
+	/* Algorithm based on 32bpp_Optimized::ResizeSprite() */
+	sprite[zoom].width  = UnScaleByZoom(sprite[ZOOM_LVL_NORMAL].width,  zoom);
+	sprite[zoom].height = UnScaleByZoom(sprite[ZOOM_LVL_NORMAL].height, zoom);
+	sprite[zoom].x_offs = UnScaleByZoom(sprite[ZOOM_LVL_NORMAL].x_offs, zoom);
+	sprite[zoom].y_offs = UnScaleByZoom(sprite[ZOOM_LVL_NORMAL].y_offs, zoom);
+
+	sprite[zoom].AllocateData(zoom, sprite[zoom].height * sprite[zoom].width);
+
+	SpriteLoader::CommonPixel *dst = sprite[zoom].data;
+	const SpriteLoader::CommonPixel *src = sprite[zoom - 1].data;
+	const SpriteLoader::CommonPixel *src_end = src + sprite[zoom - 1].height * sprite[zoom - 1].width;
+
+	for (uint y = 0; y < sprite[zoom].height; y++) {
+		if (src >= src_end) src = src_end - sprite[zoom - 1].width;
+
+		const SpriteLoader::CommonPixel *src_ln = src + sprite[zoom - 1].width * 2;
+		for (uint x = 0; x < sprite[zoom].width; x++) {
+			if (src >= src_ln) src = src_ln - 1;
+			if ((src + 1)->a != 0) { *dst = *(src + 1); }
+			else { *dst = *src; }
+			dst++;
+			src += 2;
+		}
+
+		src = src_ln;
+	}
+}
+
+static bool PadSingleSprite(SpriteLoader::Sprite *sprite, ZoomLevel zoom, uint pad_left, uint pad_top, uint pad_right, uint pad_bottom)
+{
+	uint width  = sprite->width + pad_left + pad_right;
+	uint height = sprite->height + pad_top + pad_bottom;
+
+	if (width > UINT16_MAX || height > UINT16_MAX) return false;
+
+	/* Copy source data and reallocate sprite memory. */
+	SpriteLoader::CommonPixel *src_data = MallocT<SpriteLoader::CommonPixel>(sprite->width * sprite->height);
+	MemCpyT(src_data, sprite->data, sprite->width * sprite->height);
+	sprite->AllocateData(zoom, width * height);
+
+	/* Copy with padding to destination. */
+	SpriteLoader::CommonPixel *src = src_data;
+	SpriteLoader::CommonPixel *data = sprite->data;
+	for (uint y = 0; y < height; y++) {
+		if (y < pad_top || pad_bottom + y >= height) {
+			/* Top/bottom padding. */
+			MemSetT(data, 0, width);
+			data += width;
+		} else {
+			if (pad_left > 0) {
+				/* Pad left. */
+				MemSetT(data, 0, pad_left);
+				data += pad_left;
+			}
+
+			/* Copy pixels. */
+			MemCpyT(data, src, sprite->width);
+			src += sprite->width;
+			data += sprite->width;
+
+			if (pad_right > 0) {
+				/* Pad right. */
+				MemSetT(data, 0, pad_right);
+				data += pad_right;
+			}
+		}
+	}
+	free(src_data);
+
+	/* Update sprite size. */
+	sprite->width   = width;
+	sprite->height  = height;
+	sprite->x_offs -= pad_left;
+	sprite->y_offs -= pad_top;
+
+	return true;
+}
+
+static bool PadSprites(SpriteLoader::Sprite *sprite, uint8 sprite_avail)
+{
+	int left   = sprite[ZOOM_LVL_NORMAL].x_offs;
+	int top    = sprite[ZOOM_LVL_NORMAL].y_offs;
+	int right  = sprite[ZOOM_LVL_NORMAL].x_offs + sprite[ZOOM_LVL_NORMAL].width;
+	int bottom = sprite[ZOOM_LVL_NORMAL].y_offs + sprite[ZOOM_LVL_NORMAL].height;
+
+	/* Find combined bounds of all zoom levels.*/
+	for (ZoomLevel zoom = ZOOM_LVL_OUT_2X; zoom != ZOOM_LVL_END; zoom++) {
+		if (HasBit(sprite_avail, zoom)) {
+			uint8 scaled_1 = ScaleByZoom(1, zoom);
+
+			left   = min(left, sprite[zoom].x_offs * scaled_1);
+			top    = min(top, sprite[zoom].y_offs * scaled_1);
+			right  = max(right, (sprite[zoom].x_offs + sprite[zoom].width - 1) * scaled_1);
+			bottom = max(bottom, (sprite[zoom].y_offs + sprite[zoom].height - 1) * scaled_1);
+		}
+	}
+
+	/* Pad too small sprites. */
+	SetBit(sprite_avail, ZOOM_LVL_NORMAL);
+	for (ZoomLevel zoom = ZOOM_LVL_BEGIN; zoom != ZOOM_LVL_END; zoom++) {
+		if (HasBit(sprite_avail, zoom)) {
+			int pad_left   = sprite[zoom].x_offs - UnScaleByZoom(left, zoom);
+			int pad_top    = sprite[zoom].y_offs - UnScaleByZoom(top, zoom);
+			int pad_right  = UnScaleByZoom(right, zoom) - (sprite[zoom].x_offs + sprite[zoom].width);
+			int pad_bottom = UnScaleByZoom(bottom, zoom) - (sprite[zoom].y_offs + sprite[zoom].height);
+
+			if (pad_left != 0 || pad_right != 0 || pad_top != 0 || pad_bottom != 0) {
+				if (!PadSingleSprite(&sprite[zoom], zoom, pad_left, pad_top, pad_right, pad_bottom)) return false;
+			}
+		}
+	}
+
+	return true;
+}
+
+static bool ResizeSprites(SpriteLoader::Sprite *sprite, uint8 sprite_avail, uint32 file_slot, uint32 file_pos)
+{
+	/* Create a fully zoomed image if it does not exist */
+	ZoomLevel first_avail = static_cast<ZoomLevel>(FIND_FIRST_BIT(sprite_avail));
+	if (first_avail != ZOOM_LVL_NORMAL) {
+		if (!ResizeSpriteIn(sprite, first_avail, ZOOM_LVL_NORMAL)) return false;
+	}
+
+	/* Pad sprites to make sizes match. */
+	if (!PadSprites(sprite, sprite_avail)) return false;
+
+	/* Create other missing zoom levels */
+	for (ZoomLevel zoom = ZOOM_LVL_OUT_2X; zoom != ZOOM_LVL_END; zoom++) {
+		if (HasBit(sprite_avail, zoom)) {
+			/* Check that size and offsets match the fully zoomed image. */
+			assert(sprite[zoom].width  == UnScaleByZoom(sprite[ZOOM_LVL_NORMAL].width,  zoom));
+			assert(sprite[zoom].height == UnScaleByZoom(sprite[ZOOM_LVL_NORMAL].height, zoom));
+			assert(sprite[zoom].x_offs == UnScaleByZoom(sprite[ZOOM_LVL_NORMAL].x_offs, zoom));
+			assert(sprite[zoom].y_offs == UnScaleByZoom(sprite[ZOOM_LVL_NORMAL].y_offs, zoom));
+		}
+
+		/* Zoom level is not available, or unusable, so create it */
+		if (!HasBit(sprite_avail, zoom)) ResizeSpriteOut(sprite, zoom);
+	}
+
+	return  true;
+}
+
 /**
  * Load a recolour sprite into memory.
  * @param file_slot GRF we're reading from.
@@ -208,15 +382,21 @@
 
 	DEBUG(sprite, 9, "Load sprite %d", id);
 
+	SpriteLoader::Sprite sprite[ZOOM_LVL_COUNT];
+	uint8 sprite_avail = 0;
+	sprite[ZOOM_LVL_NORMAL].type = sprite_type;
+
 	if (sprite_type == ST_NORMAL && BlitterFactoryBase::GetCurrentBlitter()->GetScreenDepth() == 32) {
 #ifdef WITH_PNG
 		/* Try loading 32bpp graphics in case we are 32bpp output */
 		SpriteLoaderPNG sprite_loader;
-		SpriteLoader::Sprite sprite;
-		sprite.type = sprite_type;
+
+		sprite_avail = sprite_loader.LoadSprite(sprite, file_slot, sc->id, sprite_type);
 
-		if (sprite_loader.LoadSprite(&sprite, file_slot, sc->id, sprite_type)) {
-			return BlitterFactoryBase::GetCurrentBlitter()->Encode(&sprite, allocator);
+		if (sprite_avail != 0) {
+			if (ResizeSprites(sprite, sprite_avail, file_slot, sc->id)) {
+				return BlitterFactoryBase::GetCurrentBlitter()->Encode(sprite, allocator);
+			}
 		}
 		/* If the PNG couldn't be loaded, fall back to 8bpp grfs */
 #else
@@ -229,10 +409,9 @@
 	}
 
 	SpriteLoaderGrf sprite_loader(sc->container_ver);
-	SpriteLoader::Sprite sprite;
-	sprite.type = sprite_type;
+	sprite_avail = sprite_loader.LoadSprite(sprite, file_slot, file_pos, sprite_type);
 
-	if (!sprite_loader.LoadSprite(&sprite, file_slot, file_pos, sprite_type)) {
+	if (sprite_avail == 0) {
 		if (sprite_type == ST_MAPGEN) return NULL;
 		if (id == SPR_IMG_QUERY) usererror("Okay... something went horribly wrong. I couldn't load the fallback sprite. What should I do?");
 		return (void*)GetRawSprite(SPR_IMG_QUERY, ST_NORMAL, allocator);
@@ -248,15 +427,15 @@
 		 * Ugly: yes. Other solution: no. Blame the original author or
 		 *  something ;) The image should really have been a data-stream
 		 *  (so type = 0xFF basicly). */
-		uint num = sprite.width * sprite.height;
+		uint num = sprite[ZOOM_LVL_NORMAL].width * sprite[ZOOM_LVL_NORMAL].height;
 
 		Sprite *s = (Sprite *)allocator(sizeof(*s) + num);
-		s->width  = sprite.width;
-		s->height = sprite.height;
-		s->x_offs = sprite.x_offs;
-		s->y_offs = sprite.y_offs;
+		s->width  = sprite[ZOOM_LVL_NORMAL].width;
+		s->height = sprite[ZOOM_LVL_NORMAL].height;
+		s->x_offs = sprite[ZOOM_LVL_NORMAL].x_offs;
+		s->y_offs = sprite[ZOOM_LVL_NORMAL].y_offs;
 
-		SpriteLoader::CommonPixel *src = sprite.data;
+		SpriteLoader::CommonPixel *src = sprite[ZOOM_LVL_NORMAL].data;
 		byte *dest = s->data;
 		while (num-- > 0) {
 			*dest++ = src->m;
@@ -266,7 +445,13 @@
 		return s;
 	}
 
-	return BlitterFactoryBase::GetCurrentBlitter()->Encode(&sprite, allocator);
+	if (sprite_type == ST_NORMAL) {
+		if (!ResizeSprites(sprite, sprite_avail, file_slot, sc->id)) {
+			if (id == SPR_IMG_QUERY) usererror("Okay... something went horribly wrong. I couldn't resize the fallback sprite. What should I do?");
+			return (void*)GetRawSprite(SPR_IMG_QUERY, ST_NORMAL, allocator);
+		}
+	}
+	return BlitterFactoryBase::GetCurrentBlitter()->Encode(sprite, allocator);
 }
 
 
@@ -704,4 +889,4 @@
 	}
 }
 
-/* static */ ReusableBuffer<SpriteLoader::CommonPixel> SpriteLoader::Sprite::buffer;
+/* static */ ReusableBuffer<SpriteLoader::CommonPixel> SpriteLoader::Sprite::buffer[ZOOM_LVL_COUNT];
diff --git a/src/spriteloader/grf.cpp b/src/spriteloader/grf.cpp
--- a/src/spriteloader/grf.cpp
+++ b/src/spriteloader/grf.cpp
@@ -59,9 +59,10 @@
  * @param sprite_type Type of the sprite we're decoding.
  * @param num Size of the decompressed sprite.
  * @param type Type of the encoded sprite.
+ * @param zoom_lvl Requested zoom level.
  * @return True if the sprite was successfully loaded.
  */
-bool DecodeSingleSprite(SpriteLoader::Sprite *sprite, uint8 file_slot, size_t file_pos, SpriteType sprite_type, int64 num, byte type)
+bool DecodeSingleSprite(SpriteLoader::Sprite *sprite, uint8 file_slot, size_t file_pos, SpriteType sprite_type, int64 num, byte type, ZoomLevel zoom_lvl)
 {
 	AutoFreePtr<byte> dest_orig(MallocT<byte>(num));
 	byte *dest = dest_orig;
@@ -96,7 +97,7 @@
 
 	if (num != 0) return WarnCorruptSprite(file_slot, file_pos, __LINE__);
 
-	sprite->AllocateData(sprite->width * sprite->height * ZOOM_LVL_BASE * ZOOM_LVL_BASE);
+	sprite->AllocateData(zoom_lvl, sprite->width * sprite->height);
 
 	/* When there are transparency pixels, this format has another trick.. decode it */
 	if (type & 0x08) {
@@ -161,22 +162,6 @@
 		}
 	}
 
-	if (ZOOM_LVL_BASE != 1 && sprite_type == ST_NORMAL) {
-		/* Simple scaling, back-to-front so that no intermediate buffers are needed. */
-		int width  = sprite->width  * ZOOM_LVL_BASE;
-		int height = sprite->height * ZOOM_LVL_BASE;
-		for (int y = height - 1; y >= 0; y--) {
-			for (int x = width - 1; x >= 0; x--) {
-				sprite->data[y * width + x] = sprite->data[y / ZOOM_LVL_BASE * sprite->width + x / ZOOM_LVL_BASE];
-			}
-		}
-
-		sprite->width  *= ZOOM_LVL_BASE;
-		sprite->height *= ZOOM_LVL_BASE;
-		sprite->x_offs *= ZOOM_LVL_BASE;
-		sprite->y_offs *= ZOOM_LVL_BASE;
-	}
-
 	/* Make sure to mark all transparent pixels transparent on the alpha channel too */
 	for (int i = 0; i < sprite->width * sprite->height; i++) {
 		if (sprite->data[i].m != 0) sprite->data[i].a = 0xFF;
@@ -185,7 +170,7 @@
 	return true;
 }
 
-bool LoadSpriteV1(SpriteLoader::Sprite *sprite, uint8 file_slot, size_t file_pos, SpriteType sprite_type)
+uint8 LoadSpriteV1(SpriteLoader::Sprite *sprite, uint8 file_slot, size_t file_pos, SpriteType sprite_type)
 {
 	/* Open the right file and go to the correct position */
 	FioSeekToFile(file_slot, file_pos);
@@ -195,24 +180,28 @@
 	byte type = FioReadByte();
 
 	/* Type 0xFF indicates either a colourmap or some other non-sprite info; we do not handle them here */
-	if (type == 0xFF) return false;
+	if (type == 0xFF) return 0;
+
+	ZoomLevel zoom_lvl = (sprite_type == ST_NORMAL) ? ZOOM_LVL_OUT_4X : ZOOM_LVL_NORMAL;
 
-	sprite->height = FioReadByte();
-	sprite->width  = FioReadWord();
-	sprite->x_offs = FioReadWord();
-	sprite->y_offs = FioReadWord();
+	sprite[zoom_lvl].height = FioReadByte();
+	sprite[zoom_lvl].width  = FioReadWord();
+	sprite[zoom_lvl].x_offs = FioReadWord();
+	sprite[zoom_lvl].y_offs = FioReadWord();
 
 	/* 0x02 indicates it is a compressed sprite, so we can't rely on 'num' to be valid.
 	 * In case it is uncompressed, the size is 'num' - 8 (header-size). */
-	num = (type & 0x02) ? sprite->width * sprite->height : num - 8;
+	num = (type & 0x02) ? sprite[zoom_lvl].width * sprite[zoom_lvl].height : num - 8;
 
-	return DecodeSingleSprite(sprite, file_slot, file_pos, sprite_type, num, type);
+	if (DecodeSingleSprite(&sprite[zoom_lvl], file_slot, file_pos, sprite_type, num, type, zoom_lvl)) return 1 << zoom_lvl;
+
+	return 0;
 }
 
-bool LoadSpriteV2(SpriteLoader::Sprite *sprite, uint8 file_slot, size_t file_pos, SpriteType sprite_type)
+uint8 LoadSpriteV2(SpriteLoader::Sprite *sprite, uint8 file_slot, size_t file_pos, SpriteType sprite_type)
 {
 	/* Is the sprite not present/stripped in the GRF? */
-	if (file_pos == SIZE_MAX) return false;
+	if (file_pos == SIZE_MAX) return 0;
 
 	/* Open the right file and go to the correct position */
 	FioSeekToFile(file_slot, file_pos);
@@ -225,27 +214,33 @@
 		byte type = FioReadByte();
 
 		/* Type 0xFF indicates either a colourmap or some other non-sprite info; we do not handle them here. */
-		if (type == 0xFF) return false;
+		if (type == 0xFF) return 0;
 
 		byte colour = type & SCC_MASK;
 		byte zoom = FioReadByte();
 
 		if (colour == SCC_PAL && zoom == 0) {
-			sprite->height = FioReadWord();
-			sprite->width  = FioReadWord();
-			sprite->x_offs = FioReadWord();
-			sprite->y_offs = FioReadWord();
+			ZoomLevel zoom_lvl = (sprite_type == ST_NORMAL) ? ZOOM_LVL_OUT_4X : ZOOM_LVL_NORMAL;
+
+			sprite[zoom_lvl].height = FioReadWord();
+			sprite[zoom_lvl].width  = FioReadWord();
+			sprite[zoom_lvl].x_offs = FioReadWord();
+			sprite[zoom_lvl].y_offs = FioReadWord();
 
 			/* Mask out colour information. */
 			type = type & ~SCC_MASK;
 
 			/* For chunked encoding we store the decompressed size in the file,
 			 * otherwise we can calculate it from the image dimensions. */
-			uint decomp_size = (type & 0x08) ? FioReadDword() : sprite->width * sprite->height;
+			uint decomp_size = (type & 0x08) ? FioReadDword() : sprite[zoom_lvl].width * sprite[zoom_lvl].height;
 
-			bool valid = DecodeSingleSprite(sprite, file_slot, file_pos, sprite_type, decomp_size, type);
-			if (FioGetPos() != start_pos + num) return WarnCorruptSprite(file_slot, file_pos, __LINE__);
-			return valid;
+			bool valid = DecodeSingleSprite(&sprite[zoom_lvl], file_slot, file_pos, sprite_type, decomp_size, type, zoom_lvl);
+			if (FioGetPos() != start_pos + num) {
+				WarnCorruptSprite(file_slot, file_pos, __LINE__);
+				return 0;
+			}
+
+			return 1 << zoom_lvl;
 		} else {
 			/* Not the wanted zoom level or colour depth, continue searching. */
 			FioSkipBytes(num - 2);
@@ -253,10 +248,10 @@
 
 	} while (FioReadDword() == id);
 
-	return false;
+	return 0;
 }
 
-bool SpriteLoaderGrf::LoadSprite(SpriteLoader::Sprite *sprite, uint8 file_slot, size_t file_pos, SpriteType sprite_type)
+uint8 SpriteLoaderGrf::LoadSprite(SpriteLoader::Sprite *sprite, uint8 file_slot, size_t file_pos, SpriteType sprite_type)
 {
 	if (this->container_ver >= 2) {
 		return LoadSpriteV2(sprite, file_slot, file_pos, sprite_type);
diff --git a/src/spriteloader/grf.hpp b/src/spriteloader/grf.hpp
--- a/src/spriteloader/grf.hpp
+++ b/src/spriteloader/grf.hpp
@@ -19,7 +19,7 @@
 	byte container_ver;
 public:
 	SpriteLoaderGrf(byte container_ver) : container_ver(container_ver) {}
-	bool LoadSprite(SpriteLoader::Sprite *sprite, uint8 file_slot, size_t file_pos, SpriteType sprite_type);
+	uint8 LoadSprite(SpriteLoader::Sprite *sprite, uint8 file_slot, size_t file_pos, SpriteType sprite_type);
 };
 
 #endif /* SPRITELOADER_GRF_HPP */
diff --git a/src/spriteloader/png.cpp b/src/spriteloader/png.cpp
--- a/src/spriteloader/png.cpp
+++ b/src/spriteloader/png.cpp
@@ -51,7 +51,7 @@
 	return false;
 }
 
-static bool LoadPNG(SpriteLoader::Sprite *sprite, const char *filename, uint32 id, volatile bool mask)
+static bool LoadPNG(SpriteLoader::Sprite *sprite, const char *filename, uint32 id, volatile bool mask, ZoomLevel zoom)
 {
 	png_byte header[8];
 	png_structp png_ptr;
@@ -115,7 +115,7 @@
 		}
 		sprite->height = height;
 		sprite->width  = width;
-		sprite->AllocateData(sprite->width * sprite->height * ZOOM_LVL_BASE * ZOOM_LVL_BASE);
+		sprite->AllocateData(zoom, sprite->width * sprite->height);
 	} else if (sprite->height != png_get_image_height(png_ptr, info_ptr) || sprite->width != png_get_image_width(png_ptr, info_ptr)) {
 		/* Make sure the mask image isn't larger than the sprite image. */
 		DEBUG(misc, 0, "Ignoring mask for SpriteID %d as it isn't the same dimension as the masked sprite", id);
@@ -206,29 +206,15 @@
 	return true;
 }
 
-bool SpriteLoaderPNG::LoadSprite(SpriteLoader::Sprite *sprite, uint8 file_slot, size_t file_pos, SpriteType sprite_type)
+uint8 SpriteLoaderPNG::LoadSprite(SpriteLoader::Sprite *sprite, uint8 file_slot, size_t file_pos, SpriteType sprite_type)
 {
-	const char *filename = FioGetFilename(file_slot);
-	if (!LoadPNG(sprite, filename, (uint32)file_pos, false)) return false;
-	if (!LoadPNG(sprite, filename, (uint32)file_pos, true)) return false;
+	ZoomLevel zoom_lvl = (sprite_type == ST_NORMAL) ? ZOOM_LVL_OUT_4X : ZOOM_LVL_NORMAL;
 
-	if (ZOOM_LVL_BASE != 1 && sprite_type == ST_NORMAL) {
-		/* Simple scaling, back-to-front so that no intermediate buffers are needed. */
-		int width  = sprite->width  * ZOOM_LVL_BASE;
-		int height = sprite->height * ZOOM_LVL_BASE;
-		for (int y = height - 1; y >= 0; y--) {
-			for (int x = width - 1; x >= 0; x--) {
-				sprite->data[y * width + x] = sprite->data[y / ZOOM_LVL_BASE * sprite->width + x / ZOOM_LVL_BASE];
-			}
-		}
+	const char *filename = FioGetFilename(file_slot);
+	if (!LoadPNG(&sprite[zoom_lvl], filename, (uint32)file_pos, false, zoom_lvl)) return 0;
+	if (!LoadPNG(&sprite[zoom_lvl], filename, (uint32)file_pos, true, zoom_lvl)) return 0;
 
-		sprite->width  *= ZOOM_LVL_BASE;
-		sprite->height *= ZOOM_LVL_BASE;
-		sprite->x_offs *= ZOOM_LVL_BASE;
-		sprite->y_offs *= ZOOM_LVL_BASE;
-	}
-
-	return true;
+	return 1 << zoom_lvl;
 }
 
 #endif /* WITH_PNG */
diff --git a/src/spriteloader/png.hpp b/src/spriteloader/png.hpp
--- a/src/spriteloader/png.hpp
+++ b/src/spriteloader/png.hpp
@@ -17,7 +17,7 @@
 /** Sprite loader for graphics coming from a PNG image. */
 class SpriteLoaderPNG : public SpriteLoader {
 public:
-	bool LoadSprite(SpriteLoader::Sprite *sprite, uint8 file_slot, size_t file_pos, SpriteType sprite_type);
+	uint8 LoadSprite(SpriteLoader::Sprite *sprite, uint8 file_slot, size_t file_pos, SpriteType sprite_type);
 };
 
 #endif /* SPRITELOADER_PNG_HPP */
diff --git a/src/spriteloader/spriteloader.hpp b/src/spriteloader/spriteloader.hpp
--- a/src/spriteloader/spriteloader.hpp
+++ b/src/spriteloader/spriteloader.hpp
@@ -43,23 +43,24 @@
 
 		/**
 		 * Allocate the sprite data of this sprite.
+		 * @param zoom Zoom level to allocate the data for.
 		 * @param size the minimum size of the data field.
 		 */
-		void AllocateData(size_t size) { this->data = Sprite::buffer.ZeroAllocate(size); }
+		void AllocateData(ZoomLevel zoom, size_t size) { this->data = Sprite::buffer[zoom].ZeroAllocate(size); }
 	private:
 		/** Allocated memory to pass sprite data around */
-		static ReusableBuffer<SpriteLoader::CommonPixel> buffer;
+		static ReusableBuffer<SpriteLoader::CommonPixel> buffer[ZOOM_LVL_COUNT];
 	};
 
 	/**
 	 * Load a sprite from the disk and return a sprite struct which is the same for all loaders.
-	 * @param sprite      The sprite to fill with data.
+	 * @param[out] sprite The sprites to fill with data.
 	 * @param file_slot   The file "descriptor" of the file we read from.
 	 * @param file_pos    The position within the file the image begins.
 	 * @param sprite_type The type of sprite we're trying to load.
-	 * @return true iff loading went okay.
+	 * @return Bit mask of the zoom levels successfully loaded or 0 if no sprite could be loaded.
 	 */
-	virtual bool LoadSprite(SpriteLoader::Sprite *sprite, uint8 file_slot, size_t file_pos, SpriteType sprite_type) = 0;
+	virtual uint8 LoadSprite(SpriteLoader::Sprite *sprite, uint8 file_slot, size_t file_pos, SpriteType sprite_type) = 0;
 
 	virtual ~SpriteLoader() { }
 };