Pass a transformation matrix in CommonRotation shaders instead of an angle

This will allow us to implement shearing more easily. Also, for the non-SmearRotxel shaders, normalize their pivot in GDScript, before passing it to the script. Should probably be faster this way

src/Shaders/Effects/Rotation/CommonRotation.gdshaderinc

@@ -1,22 +1,14 @@
 uniform sampler2D selection_tex : filter_nearest;
-uniform vec2 pivot_pixel;
-uniform float angle;
+uniform vec2 pivot;
+uniform mat2 transformation_matrix;
 
-vec2 rotate(vec2 uv, vec2 pivot, float ratio) {
+vec2 rotate(vec2 uv, float ratio) {
 	// Scale and center image
-	uv.x -= pivot.x;
-	uv.x *= ratio;
-	uv.x += pivot.x;
+	uv.x = (uv.x - pivot.x) * ratio + pivot.x;
+	uv -= pivot;
 
 	// Rotate image
-	uv -= pivot;
-	mat3 transformation = mat3(
-		vec3(cos(angle), -sin(angle), 0.0),
-		vec3(sin(angle), cos(angle), 0.0),
-		vec3(0.0, 0.0, 1.0)
-	);
-
-	uv = (transformation * vec3(uv, 1.0)).xy;
+	uv *= transformation_matrix;
 	uv.x /= ratio;
 	uv += pivot;
 

src/Shaders/Effects/Rotation/NearestNeighbour.gdshader

@@ -8,10 +8,9 @@ void fragment() {
 	vec4 original = texture(TEXTURE, UV);
 	vec2 tex_size = 1.0 / TEXTURE_PIXEL_SIZE; // Texture size in real pixel coordinates
 	vec2 pixelated_uv = floor(UV * tex_size) / (tex_size - 1.0); // Pixelate UV to fit resolution
-	vec2 pivot = pivot_pixel / tex_size; // Normalize pivot position
 	float ratio = tex_size.x / tex_size.y; // Resolution ratio
 
-	vec2 rotated_uv = rotate(pixelated_uv, pivot, ratio);
+	vec2 rotated_uv = rotate(pixelated_uv, ratio);
 	vec4 rotated_color = texture(TEXTURE, rotated_uv); // Rotated image
 	COLOR = mix_rotated_and_original(rotated_color, original, UV, rotated_uv, TEXTURE_PIXEL_SIZE);
 }

src/Shaders/Effects/Rotation/OmniScale.gdshader

@@ -292,15 +292,14 @@ void fragment()
 {
 	vec4 original = texture(TEXTURE, UV);
 	vec2 size = 1.0 / TEXTURE_PIXEL_SIZE;
-	vec2 pivot = pivot_pixel / size; // Normalize pivot position
 	float ratio = size.x / size.y; // Resolution ratio
 	vec2 pixelated_uv = floor(UV * size) / (size - 1.0); // Pixelate UV to fit resolution
 	vec2 rotated_uv;
 	if (preview) {
-		rotated_uv = rotate(pixelated_uv, pivot, ratio);
+		rotated_uv = rotate(pixelated_uv, ratio);
 	}
 	else {
-		rotated_uv = rotate(UV, pivot, ratio);
+		rotated_uv = rotate(UV, ratio);
 	}
 	vec4 c = scale(TEXTURE, rotated_uv, TEXTURE_PIXEL_SIZE);
 

src/Shaders/Effects/Rotation/SmearRotxel.gdshader

@@ -6,7 +6,7 @@ uniform sampler2D selection_tex : filter_nearest;
 uniform float initial_angle = 0.0;
 uniform float ending_angle = 0.0;
 uniform float tolerance : hint_range(0.0, 255.0) = 100.0;
-uniform vec2 origin = vec2(0.0, 0.0);
+uniform vec2 pivot = vec2(0.0, 0.0);
 uniform vec2 position = vec2(0.0, 0.0);
 
 bool similarColors(vec4 c1, vec4 c2) {
@@ -16,7 +16,7 @@ bool similarColors(vec4 c1, vec4 c2) {
 
 vec4 rotate(sampler2D tex, vec2 uv, vec2 tex_pixel_size) {
 	vec4 color = vec4(0.0);
-	vec2 center = origin / tex_pixel_size;
+	vec2 center = pivot / tex_pixel_size;
 	vec2 size = 1.0 / tex_pixel_size;
 	vec2 coord = uv / tex_pixel_size + position;
 	int dx = 3 * (int(coord.x) - int(center.x));
@@ -113,7 +113,7 @@ vec4 rotate(sampler2D tex, vec2 uv, vec2 tex_pixel_size) {
 // The exact same as rotate, but had to be re-defined due to https://github.com/godotengine/godot/issues/75935
 vec4 rotate_uniform(sampler2D tex, vec2 uv, vec2 tex_pixel_size) {
 	vec4 color = vec4(0.0);
-	vec2 center = origin / tex_pixel_size;
+	vec2 center = pivot / tex_pixel_size;
 	vec2 size = 1.0 / tex_pixel_size;
 	vec2 coord = uv / tex_pixel_size + position;
 	int dx = 3 * (int(coord.x) - int(center.x));

src/Shaders/Effects/Rotation/cleanEdge.gdshader

@@ -275,15 +275,14 @@ void fragment() {
 	vec2 size = 1.0/TEXTURE_PIXEL_SIZE+0.0001; //fix for some sort of rounding error
 	// Pixelorama edit
 	vec4 original = texture(TEXTURE, UV);
-	vec2 pivot = pivot_pixel / size; // Normalize pivot position
 	float ratio = size.x / size.y; // Resolution ratio
 	vec2 pixelated_uv = floor(UV * size) / (size - 1.0); // Pixelate UV to fit resolutio
 	vec2 rotated_uv;
 	if (preview) {
-		rotated_uv = rotate(pixelated_uv, pivot, ratio);
+		rotated_uv = rotate(pixelated_uv, ratio);
 	}
 	else {
-		rotated_uv = rotate(UV, pivot, ratio);
+		rotated_uv = rotate(UV, ratio);
 	}
 	vec2 px = rotated_uv * size;
 	vec2 local = fract(px);

src/UI/Dialogs/ImageEffects/RotateImage.gd

@@ -99,17 +99,16 @@ func commit_action(cel: Image, _project := Global.current_project) -> void:
 	if _type_is_shader():
 		var shader := rotxel_shader
 		var params := {
-			"angle": angle, "selection_tex": selection_tex, "pivot_pixel": pivot, "preview": true
+			"transformation_matrix": Transform2D(angle, Vector2.ZERO),
+			"selection_tex": selection_tex,
+			"pivot": pivot / Vector2(cel.get_size()),
+			"preview": true
 		}
 		match type_option_button.get_selected_id():
 			ROTXEL_SMEAR:
-				params = {
-					"initial_angle": init_angle,
-					"ending_angle": angle,
-					"tolerance": tolerance_slider.value,
-					"selection_tex": selection_tex,
-					"origin": pivot / Vector2(cel.get_size()),
-				}
+				params["ending_angle"] = angle
+				params["initial_angle"] = init_angle
+				params["tolerance"] = tolerance_slider.value
 			CLEANEDGE:
 				shader = DrawingAlgos.clean_edge_shader
 			OMNISCALE: