Make rectangles zoom together with the grid

1 files changed, 130 insertions, 0 deletions

diff --git a/src/transform.rs b/src/transform.rs
new file mode 100644
index 0000000..ef94029
--- /dev/null
+++ b/src/transform.rs
@@ -0,0 +1,130 @@
+//! Transformation module
+//!
+//! Useful to turn on-screen coordinates into the measurements in the "real" world the map
+//! describes and the other way around.
+
+use piston_window::math;
+
+const STANDARD_PIXELS_PER_M: f64 = 64.;
+const MIN_PIXELS_PER_M: f64 = 0.5;
+const MAX_PIXELS_PER_M: f64 = 10_000.;
+
+pub struct Transform {
+    /// The (not necessarily natural) number of pixels per m, i.e. the current scale of the map
+    pixels_per_m: f64,
+    /// The vector the entire on-screen map is moved by in pixels
+    translation_px: [f64; 2],
+}
+
+impl Transform {
+    /// Create a new standard transformation for the map.
+    pub fn new() -> Self {
+        Self {
+            pixels_per_m: STANDARD_PIXELS_PER_M,
+            translation_px: [0., 0.],
+        }
+    }
+
+    /// Convert a point that is given in meters into the corresponding point in pixels.
+    #[inline]
+    pub fn point_m_to_px(&self, point: [f64; 2]) -> [f64; 2] {
+        // Start by converting the absolute position in meters into the absolute position in
+        // pixels, then add the translation of the screen.
+        math::add(
+            math::mul_scalar(point, self.pixels_per_m),
+            self.translation_px,
+        )
+    }
+
+    /// Convert an on-screen point into an absolute point with values in meters.
+    #[inline]
+    pub fn point_px_to_m(&self, point: [f64; 2]) -> [f64; 2] {
+        // Start by subtracting the pixel translation and afterwards convert these absolute pixel
+        // measurements into meters.
+        math::mul_scalar(
+            math::sub(point, self.translation_px),
+            1. / self.pixels_per_m,
+        )
+    }
+
+    /// Convert a length given in meters into a length in pixels
+    #[inline]
+    pub fn length_m_to_px(&self, length: f64) -> f64 {
+        length * self.pixels_per_m
+    }
+
+    /// Convert a length given in pixels into a length in meters
+    #[inline]
+    pub fn length_px_to_m(&self, length: f64) -> f64 {
+        length / self.pixels_per_m
+    }
+
+    /// Convert a rectangle which has measurements in meters into one of pixels
+    #[inline]
+    pub fn rect_m_to_px(&self, rect: [f64; 4]) -> [f64; 4] {
+        let left_upper = self.point_m_to_px([rect[0], rect[1]]);
+        [
+            left_upper[0],
+            left_upper[1],
+            self.length_m_to_px(rect[2]),
+            self.length_m_to_px(rect[3]),
+        ]
+    }
+
+    /// Convert a rectangle which has measurements in pixels into one of meters
+    #[inline]
+    pub fn rect_px_to_m(&self, rect: [f64; 4]) -> [f64; 4] {
+        let left_upper = self.point_px_to_m([rect[0], rect[1]]);
+        [
+            left_upper[0],
+            left_upper[1],
+            self.length_px_to_m(rect[2]),
+            self.length_px_to_m(rect[3]),
+        ]
+    }
+
+    /* Helper function to make sure the standard zoom factor is always exact. This helps
+     * normalising zoom levels even when the user zooms in and out extremely often, assuming they
+     * pass the standard zoom factor.
+     */
+    fn normalise_zoom(&mut self) {
+        if self.pixels_per_m > STANDARD_PIXELS_PER_M - 5.
+            && self.pixels_per_m < STANDARD_PIXELS_PER_M + 5.
+        {
+            self.pixels_per_m = STANDARD_PIXELS_PER_M;
+        }
+    }
+
+    /// Attempts to zoom in a step and return true.
+    /// If the maximum zoom is reached, this function changes nothing and returns false.
+    pub fn try_zoom_in(&mut self) -> bool {
+        // TODO: Zoom in on mouse pointer position
+        if self.pixels_per_m < MAX_PIXELS_PER_M {
+            self.pixels_per_m *= 1.2;
+            self.normalise_zoom();
+            true
+        } else {
+            false
+        }
+    }
+
+    /// Attempts to zoom out a step and return true.
+    /// If the minimum zoom is reached, this function changes nothing and returns false.
+    pub fn try_zoom_out(&mut self) -> bool {
+        // TODO: Zoom out at mouse pointer position
+        if self.pixels_per_m > MIN_PIXELS_PER_M {
+            self.pixels_per_m /= 1.2;
+            self.normalise_zoom();
+            true
+        } else {
+            false
+        }
+    }
+
+    pub fn pixels_per_m(&self) -> f64 {
+        self.pixels_per_m
+    }
+    pub fn translation_px(&self) -> [f64; 2] {
+        self.translation_px
+    }
+}