71 lines
2.2 KiB
Rust
71 lines
2.2 KiB
Rust
//! This file implements the "rotation as shearing" algorithm.
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//!
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//! The algorithm can rotate images without making use of any trigonometric
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//! functions (or working with floats altogether, assuming you don't care
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//! about antialiasing).
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//!
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//! For more information, consult this article:
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//! https://www.ocf.berkeley.edu/~fricke/projects/israel/paeth/rotation_by_shearing.html
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use image::{DynamicImage, GenericImage, GenericImageView};
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use crate::bitmap::{Position, Rect};
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fn unsigned_in_bounds(image: &DynamicImage, x: i32, y: i32) -> bool {
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x >= 0 && y >= 0 && image.in_bounds(x as u32, y as u32)
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}
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/// Performs a horizontal shear operation, without performing anti-aliasing
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pub fn xshear(image: &mut DynamicImage, rect: Rect, center: Position, shear: f32) {
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let width = rect.width as i32;
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for y in rect.y..rect.y + rect.height as i32 {
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let skew = (shear * ((y - center.1) as f32)) as i32;
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for i in rect.x..rect.x + width {
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let x = if skew < 0 {
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i
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} else {
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2 * rect.x + width - 1 - i
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};
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if unsigned_in_bounds(image, x, y) {
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let pixel = image.get_pixel(x as u32, y as u32);
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if unsigned_in_bounds(image, x + skew, y) {
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image.put_pixel((x + skew) as u32, y as u32, pixel);
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};
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};
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}
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}
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}
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/// Performs a vertical shear operation, without performing anti-aliasing
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pub fn yshear(image: &mut DynamicImage, rect: Rect, center: Position, shear: f32) {
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let height = rect.height as i32;
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for x in rect.x..rect.x + rect.width as i32 {
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let skew = (shear * ((x - center.0) as f32)) as i32;
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for i in rect.y..rect.y + height {
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let y = if skew < 0 {
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i
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} else {
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2 * rect.y + height - 1 - i
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};
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if unsigned_in_bounds(image, x, y) {
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let pixel = image.get_pixel(x as u32, y as u32);
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if unsigned_in_bounds(image, x, y + skew) {
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image.put_pixel(x as u32, (y + skew) as u32, pixel);
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};
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};
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}
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}
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}
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/// Performs a rotation as a series of three shear operations.
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/// Does not perform anti-aliasing.
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pub fn rotate(image: &mut DynamicImage, rect: Rect, center: Position, angle: f32) {
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let alpha = -f32::tan(angle / 2.0);
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let beta = f32::sin(angle);
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xshear(image, rect, center, alpha);
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yshear(image, rect, center, beta);
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xshear(image, rect, center, alpha);
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}
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