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```//! Transformation context

use DrawState;
use math::{
abs_transform,
identity,
get_scale,
scale,
Matrix2d,
Scalar,
Vec2d,
};
use Viewport;

/// Drawing 2d context.
#[derive(Copy, Clone)]
pub struct Context {
/// Viewport information.
pub viewport: Option<Viewport>,
/// View transformation.
pub view: Matrix2d,
/// Current transformation.
pub transform: Matrix2d,
/// Current draw state settings.
pub draw_state: DrawState,
}

impl Context {
/// Creates a new drawing context.
#[inline(always)]
pub fn new() -> Context {
Context {
view: identity(),
transform: identity(),
draw_state: Default::default(),
viewport: None,
}
}

/// Creates a new context with absolute transform in point coordinates.
///
/// This function assumes the default coordinate system
/// being centered with x axis pointing to the right
/// and y axis pointing up.
///
/// Returns a drawing context
/// with origin in the upper left corner
/// and x axis pointing to the right
/// and y axis pointing down.
#[inline(always)]
pub fn new_viewport(viewport: Viewport) -> Context {
let mat = viewport.abs_transform();
Context {
view: mat,
transform: mat,
draw_state: Default::default(),
viewport: Some(viewport),
}
}

/// Creates a new drawing context in absolute coordinates.
///
/// This function assumes the default coordinate system
/// being centered with x axis pointing to the right
/// and y axis pointing up.
///
/// Returns a drawing context
/// with origin in the upper left corner
/// and x axis pointing to the right
/// and y axis pointing down.
#[inline(always)]
pub fn new_abs(w: Scalar, h: Scalar) -> Context {
let mat = abs_transform(w, h);
Context {
view: mat,
transform: mat,
draw_state: Default::default(),
viewport: None,
}
}

/// Moves the current transform to the view coordinate system.
///
/// This is usually [0.0, 0.0] in the upper left corner
/// with the x axis pointing to the right
/// and the y axis pointing down.
#[inline(always)]
pub fn view(mut self) -> Self {
self.transform = self.view;
self
}

/// Moves the current transform to the default coordinate system.
///
/// This is usually [0.0, 0.0] in the center
/// with the x axis pointing to the right
/// and the y axis pointing up.
#[inline(always)]
pub fn reset(mut self) -> Self {
self.transform = identity();
self
}

/// Stores the current transform as new view.
#[inline(always)]
pub fn store_view(mut self) -> Self {
self.view = self.transform;
self
}

/// Computes the current view size.
#[inline(always)]
pub fn get_view_size(&self) -> Vec2d {
let scale = get_scale(self.view);
[2.0 / scale[0], 2.0 / scale[1]]
}
}

#[cfg(test)]
mod test {
use super::Context;

#[test]
fn test_context() {
use Transformed;

let c = Context::new();
{
let d = c.trans(20.0, 40.0);
let d = d.trans(10.0, 10.0);
let transform = d.transform;
assert_eq!(transform[0][2], 30.0);
assert_eq!(transform[1][2], 50.0);
}

let transform = c.transform;
assert_eq!(transform[0][2], 0.0);
assert_eq!(transform[1][2], 0.0);

let c = c.rot_deg(90.0);
let transform = c.transform;
assert!((transform[0][0] - 0.0).abs() < 0.00001);
assert!((transform[0][1] + 1.0).abs() < 0.00001);
}

#[test]
fn test_scale() {
use Transformed;

let c = Context::new();
let c = c.scale(2.0, 3.0);
let transform = c.transform;
assert!((transform[0][0] - 2.0).abs() < 0.00001);
assert!((transform[1][1] - 3.0).abs() < 0.00001);
}
}
```