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use Matrix;

/// Trait for a context that can handle drawing.
pub trait Draw {
    /// Type of a resource that represents an image.
    type ImageResource: ?Sized;

    /// Type of a resource that represents a font.
    type FontResource: ?Sized;

    /// Draws a single triangle that covers the top-left hand corner of the surface, multiplied
    /// by the matrix. In other words, the OpenGL positions of the triangle are `[-1.0, 1.0]`,
    /// `[-1.0, -1.0]` and `[1.0, 1.0]`.
    ///
    /// The UV coordinates correspond to the UV coordinates of the texture. `[0.0, 0.0]` is the
    /// bottom-left hand corner of the texture, and `[1.0, 1.0]` is the top-right hand corner.
    fn draw_triangle(&mut self, texture: &Self::ImageResource, matrix: &Matrix,
                     uv_coords: [[f32; 2]; 3]);

    /// Draws an image that covers the whole surface (from `-1.0` to `1.0` both horizontally and
    /// vertically), but multiplied by the matrix.
    ///
    /// This function should not try to preseve the aspect ratio of the image. This is handled by
    /// the caller.
    #[inline]
    fn draw_image(&mut self, name: &Self::ImageResource, matrix: &Matrix) {
        self.draw_image_uv(name, matrix, [0.0, 1.0], [1.0, 1.0], [1.0, 0.0], [0.0, 0.0])
    }

    /// Draws an image that covers the whole surface (from `-1.0` to `1.0` both horizontally and
    /// vertically), but multiplied by the matrix.
    ///
    /// This function should not try to preseve the aspect ratio of the image. This is handled by
    /// the caller.
    ///
    /// Contrary to `draw_image`, this library allows one to specify UV coordinates of the four
    /// borders. Coordinates `[0.0, 0.0]` correspond to the bottom-left hand corner of the
    /// image, and `[1.0, 1.0]` correspond to the top-right hand corner.
    #[inline]
    fn draw_image_uv(&mut self, name: &Self::ImageResource, matrix: &Matrix, top_left: [f32; 2],
                     top_right: [f32; 2], bottom_right: [f32; 2], bottom_left: [f32; 2])
    {
        self.draw_triangle(name, matrix, [top_left, bottom_left, top_right]);

        let invert = Matrix::scale(-1.0);
        self.draw_triangle(name, &(*matrix * invert), [bottom_right, top_right, bottom_left]);
    }

    /// Given an image, this functions returns its width divided by its height.
    fn get_image_width_per_height(&mut self, name: &Self::ImageResource) -> f32;

    /// Draws an image that covers the whole surface (from `-1.0` to `1.0` both horizontally and
    /// vertically), but multiplied by the matrix.
    ///
    /// This function should not try to preseve the aspect ratio of the text. This is handled by
    /// the caller.
    fn draw_text(&mut self, font: &Self::FontResource, matrix: &Matrix, text: &str,
                 rgb_color: [f32; 3]);

    /// Given a font and a text, this function returns the width the text would have on the screen,
    /// divided by the size of a EM.
    fn get_text_width_per_em(&mut self, font: &Self::FontResource, text: &str) -> f32;
}