`Image` Fix `rotate_90`/`rotate_180` methods

1 files changed, 103 insertions, 53 deletions

diff --git a/core/io/image.cpp b/core/io/image.cpp
index 2d87523ca4..bd209b7c68 100644
--- a/core/io/image.cpp
+++ b/core/io/image.cpp
@@ -1341,78 +1341,126 @@ void Image::crop(int p_width, int p_height) {
 
 void Image::rotate_90(ClockDirection p_direction) {
 	ERR_FAIL_COND_MSG(!_can_modify(format), "Cannot rotate in compressed or custom image formats.");
-	ERR_FAIL_COND_MSG(width <= 1, "The Image width specified (" + itos(width) + " pixels) must be greater than 1 pixels.");
-	ERR_FAIL_COND_MSG(height <= 1, "The Image height specified (" + itos(height) + " pixels) must be greater than 1 pixels.");
-
-	int saved_width = height;
-	int saved_height = width;
-
-	if (width != height) {
-		int n = MAX(width, height);
-		resize(n, n, INTERPOLATE_NEAREST);
-	}
+	ERR_FAIL_COND_MSG(width <= 0, "The Image width specified (" + itos(width) + " pixels) must be greater than 0 pixels.");
+	ERR_FAIL_COND_MSG(height <= 0, "The Image height specified (" + itos(height) + " pixels) must be greater than 0 pixels.");
 
 	bool used_mipmaps = has_mipmaps();
 	if (used_mipmaps) {
 		clear_mipmaps();
 	}
 
+	// In-place 90 degrees rotation by following the permutation cycles.
 	{
-		uint8_t *w = data.ptrw();
-		uint8_t src[16];
-		uint8_t dst[16];
+		// Explanation by example (clockwise):
+		//
+		//  abc      da
+		//  def  ->  eb
+		//           fc
+		//
+		// In memory:
+		//  012345    012345
+		//  abcdef -> daebfc
+		//
+		// Permutation cycles:
+		//  (0  --a-->  1  --b-->  3  --d-->  0)
+		//  (2  --c-->  5  --f-->  4  --e-->  2)
+		//
+		// Applying cycles (backwards):
+		//  0->s  s=a (store)
+		//  3->0  abcdef -> dbcdef
+		//  1->3  dbcdef -> dbcbef
+		//  s->1  dbcbef -> dacbef
+		//
+		//  2->s  s=c
+		//  4->2  dacbef -> daebef
+		//  5->4  daebef -> daebff
+		//  s->5  daebff -> daebfc
+
+		const int w = width;
+		const int h = height;
+		const int size = w * h;
+
+		uint8_t *data_ptr = data.ptrw();
 		uint32_t pixel_size = get_format_pixel_size(format);
 
-		// Flip.
+		uint8_t single_pixel_buffer[16];
 
-		if (p_direction == CLOCKWISE) {
-			for (int y = 0; y < height / 2; y++) {
-				for (int x = 0; x < width; x++) {
-					_get_pixelb(x, y, pixel_size, w, src);
-					_get_pixelb(x, height - y - 1, pixel_size, w, dst);
+#define PREV_INDEX_IN_CYCLE(index) (p_direction == CLOCKWISE) ? ((h - 1 - (index % h)) * w + (index / h)) : ((index % h) * w + (w - 1 - (index / h)))
 
-					_put_pixelb(x, height - y - 1, pixel_size, w, src);
-					_put_pixelb(x, y, pixel_size, w, dst);
+		if (w == h) { // Square case, 4-length cycles only (plus irrelevant thus skipped 1-length cycle in the middle for odd-sized squares).
+			for (int y = 0; y < h / 2; y++) {
+				for (int x = 0; x < (w + 1) / 2; x++) {
+					int current = y * w + x;
+					memcpy(single_pixel_buffer, data_ptr + current * pixel_size, pixel_size);
+					for (int i = 0; i < 3; i++) {
+						int prev = PREV_INDEX_IN_CYCLE(current);
+						memcpy(data_ptr + current * pixel_size, data_ptr + prev * pixel_size, pixel_size);
+						current = prev;
+					}
+					memcpy(data_ptr + current * pixel_size, single_pixel_buffer, pixel_size);
 				}
 			}
-		} else {
-			for (int y = 0; y < height; y++) {
-				for (int x = 0; x < width / 2; x++) {
-					_get_pixelb(x, y, pixel_size, w, src);
-					_get_pixelb(width - x - 1, y, pixel_size, w, dst);
+		} else { // Rectangular case (w != h), kinda unpredictable cycles.
+			int permuted_pixels_count = 0;
+
+			for (int i = 0; i < size; i++) {
+				int prev = PREV_INDEX_IN_CYCLE(i);
+				if (prev == i) {
+					// 1-length cycle, pixel remains at the same index.
+					permuted_pixels_count++;
+					continue;
+				}
 
-					_put_pixelb(width - x - 1, y, pixel_size, w, src);
-					_put_pixelb(x, y, pixel_size, w, dst);
+				// Check whether we already processed this cycle.
+				// We iterate over it and if we'll find an index smaller than `i` then we already
+				// processed this cycle because we always start at the smallest index in the cycle.
+				// TODO: Improve this naive approach, can be done better.
+				while (prev > i) {
+					prev = PREV_INDEX_IN_CYCLE(prev);
+				}
+				if (prev < i) {
+					continue;
 				}
-			}
-		}
 
-		// Transpose.
+				// Save the in-cycle pixel with the smallest index (`i`).
+				memcpy(single_pixel_buffer, data_ptr + i * pixel_size, pixel_size);
 
-		for (int y = 0; y < height; y++) {
-			for (int x = 0; x < width; x++) {
-				if (x < y) {
-					_get_pixelb(x, y, pixel_size, w, src);
-					_get_pixelb(y, x, pixel_size, w, dst);
+				// Overwrite pixels one by one by the preceding pixel in the cycle.
+				int current = i;
+				prev = PREV_INDEX_IN_CYCLE(current);
+				while (prev != i) {
+					memcpy(data_ptr + current * pixel_size, data_ptr + prev * pixel_size, pixel_size);
+					permuted_pixels_count++;
 
-					_put_pixelb(y, x, pixel_size, w, src);
-					_put_pixelb(x, y, pixel_size, w, dst);
+					current = prev;
+					prev = PREV_INDEX_IN_CYCLE(current);
+				};
+
+				// Overwrite the remaining pixel in the cycle by the saved pixel with the smallest index.
+				memcpy(data_ptr + current * pixel_size, single_pixel_buffer, pixel_size);
+				permuted_pixels_count++;
+
+				if (permuted_pixels_count == size) {
+					break;
 				}
 			}
+
+			width = h;
+			height = w;
 		}
+
+#undef PREV_INDEX_IN_CYCLE
 	}
 
-	if (saved_width != saved_height) {
-		resize(saved_width, saved_height, INTERPOLATE_NEAREST);
-	} else if (used_mipmaps) {
+	if (used_mipmaps) {
 		generate_mipmaps();
 	}
 }
 
 void Image::rotate_180() {
 	ERR_FAIL_COND_MSG(!_can_modify(format), "Cannot rotate in compressed or custom image formats.");
-	ERR_FAIL_COND_MSG(width <= 1, "The Image width specified (" + itos(width) + " pixels) must be greater than 1 pixels.");
-	ERR_FAIL_COND_MSG(height <= 1, "The Image height specified (" + itos(height) + " pixels) must be greater than 1 pixels.");
+	ERR_FAIL_COND_MSG(width <= 0, "The Image width specified (" + itos(width) + " pixels) must be greater than 0 pixels.");
+	ERR_FAIL_COND_MSG(height <= 0, "The Image height specified (" + itos(height) + " pixels) must be greater than 0 pixels.");
 
 	bool used_mipmaps = has_mipmaps();
 	if (used_mipmaps) {
@@ -1420,19 +1468,21 @@ void Image::rotate_180() {
 	}
 
 	{
-		uint8_t *w = data.ptrw();
-		uint8_t src[16];
-		uint8_t dst[16];
+		uint8_t *data_ptr = data.ptrw();
 		uint32_t pixel_size = get_format_pixel_size(format);
 
-		for (int y = 0; y < height / 2; y++) {
-			for (int x = 0; x < width; x++) {
-				_get_pixelb(x, y, pixel_size, w, src);
-				_get_pixelb(width - x - 1, height - y - 1, pixel_size, w, dst);
+		uint8_t single_pixel_buffer[16];
 
-				_put_pixelb(width - x - 1, height - y - 1, pixel_size, w, src);
-				_put_pixelb(x, y, pixel_size, w, dst);
-			}
+		uint8_t *from_begin_ptr = data_ptr;
+		uint8_t *from_end_ptr = data_ptr + (width * height - 1) * pixel_size;
+
+		while (from_begin_ptr < from_end_ptr) {
+			memcpy(single_pixel_buffer, from_begin_ptr, pixel_size);
+			memcpy(from_begin_ptr, from_end_ptr, pixel_size);
+			memcpy(from_end_ptr, single_pixel_buffer, pixel_size);
+
+			from_begin_ptr += pixel_size;
+			from_end_ptr -= pixel_size;
 		}
 	}