Struct sdl2::render::Canvas

pub struct Canvas<T: RenderTarget> { /* private fields */ }

Manages and owns a target (Surface or Window) and allows drawing in it.

If the Window manipulates the shell of the Window, Canvas<Window> allows you to manipulate both the shell and the inside of the window; you can manipulate pixel by pixel (not recommended), lines, colored rectangles, or paste Textures to this Canvas.

Drawing to the Canvas does not take effect immediately, it draws to a buffer until you call present(), where all the operations you did until the last present() are updated to your target

Its context may be shared with the TextureCreator.

The context will not be dropped until all references of it are out of scope.

Examples

let window = video_subsystem.window("Example", 800, 600).build().unwrap();

// Let's create a Canvas which we will use to draw in our Window
let mut canvas : Canvas<Window> = window.into_canvas()
    .present_vsync() //< this means the screen cannot
    // render faster than your display rate (usually 60Hz or 144Hz)
    .build().unwrap();

canvas.set_draw_color(Color::RGB(0, 0, 0));
// fills the canvas with the color we set in `set_draw_color`.
canvas.clear();

// change the color of our drawing with a gold-color ...
canvas.set_draw_color(Color::RGB(255, 210, 0));
// A draw a rectangle which almost fills our window with it !
canvas.fill_rect(Rect::new(10, 10, 780, 580));

// However the canvas has not been updated to the window yet,
// everything has been processed to an internal buffer,
// but if we want our buffer to be displayed on the window,
// we need to call `present`. We need to call this every time
// we want to render a new frame on the window.
canvas.present();
// present does not "clear" the buffer, that means that
// you have to clear it yourself before rendering again,
// otherwise leftovers of what you've renderer before might
// show up on the window !
//
// A good rule of thumb is to `clear()`, draw every texture
// needed, and then `present()`; repeat this every new frame.

Implementations

impl<'s> Canvas<Surface<'s>>

Methods for the SurfaceCanvas.

pub fn from_surface(surface: Surface<'s>) -> Result<Self, String>

Creates a 2D software rendering context for a surface.

This method should only fail if SDL2 is not built with rendering support, or there’s an out-of-memory error.

pub fn surface(&self) -> &SurfaceRef

Gets a reference to the associated surface of the Canvas

pub fn surface_mut(&mut self) -> &mut SurfaceRef

Gets a mutable reference to the associated surface of the Canvas

pub fn into_surface(self) -> Surface<'s>

Gets the associated surface of the Canvas and destroys the Canvas

pub fn texture_creator(&self) -> TextureCreator<SurfaceContext<'s>>

Returns a TextureCreator that can create Textures to be drawn on this Canvas

This TextureCreator will share a reference to the renderer and target context.

The target (i.e., Window) will not be destroyed and the SDL_Renderer will not be destroyed if the TextureCreator is still in scope.

impl Canvas<Window>

Methods for the WindowCanvas.

pub fn window(&self) -> &Window

Gets a reference to the associated window of the Canvas

pub fn window_mut(&mut self) -> &mut Window

Gets a mutable reference to the associated window of the Canvas

pub fn into_window(self) -> Window

Gets the associated window of the Canvas and destroys the Canvas

pub fn default_pixel_format(&self) -> PixelFormatEnum

pub fn texture_creator(&self) -> TextureCreator<WindowContext>

Returns a TextureCreator that can create Textures to be drawn on this Canvas

This TextureCreator will share a reference to the renderer and target context.

The target (i.e., Window) will not be destroyed and the SDL_Renderer will not be destroyed if the TextureCreator is still in scope.

impl<T: RenderTarget> Canvas<T>

pub fn render_target_supported(&self) -> bool

Determine whether a window supports the use of render targets.

pub fn with_texture_canvas<F>(
    &mut self,
    texture: &mut Texture<'_>,
    f: F
) -> Result<(), TargetRenderError>where
    for<'r> F: FnOnce(&'r mut Canvas<T>),

Temporarily sets the target of Canvas to a Texture. This effectively allows rendering to a Texture in any way you want: you can make a Texture a combination of other Textures, be a complex geometry form with the gfx module, … You can draw pixel by pixel in it if you want, so you can do basically anything with that Texture.

If you want to set the content of multiple Texture at once the most efficient way possible, don’t make a loop and call this function every time and use with_multiple_texture_canvas instead. Using with_texture_canvas is actually inefficient because the target is reset to the source (the Window or the Surface) at the end of this function, but using it in a loop would make this reset useless. Plus, the check that render_target is actually supported on that Canvas is also done every time, leading to useless checks.

Notes

Note that the Canvas in the closure is exactly the same as the one you call this function with, meaning that you can call every function of your original Canvas.

That means you can also call with_texture_canvas and with_multiple_texture_canvas from the inside of the closure. Even though this is useless and inefficient, this is totally safe to do and allowed.

Since the render target is now a Texture, some calls of Canvas might return another result than if the target was to be the original source. For instance output_size will return this size of the current Texture in the closure, but the size of the Window or Surface outside of the closure.

You do not need to call present after drawing in the Canvas in the closure, the changes are applied directly to the Texture instead of a hidden buffer.

Errors

• returns TargetRenderError::NotSupported if the renderer does not support the use of render targets
• returns TargetRenderError::SdlError if SDL2 returned with an error code.

The texture must be created with the texture access: sdl2::render::TextureAccess::Target. Using a texture which was not created with the texture access Target is undefined behavior.

Examples

The example below changes a newly created Texture to be a 150-by-150 black texture with a 50-by-50 red square in the middle.

let texture_creator = canvas.texture_creator();
let mut texture = texture_creator
    .create_texture_target(texture_creator.default_pixel_format(), 150, 150)
    .unwrap();
let result = canvas.with_texture_canvas(&mut texture, |texture_canvas| {
    texture_canvas.set_draw_color(Color::RGBA(0, 0, 0, 255));
    texture_canvas.clear();
    texture_canvas.set_draw_color(Color::RGBA(255, 0, 0, 255));
    texture_canvas.fill_rect(Rect::new(50, 50, 50, 50)).unwrap();
});

pub fn with_multiple_texture_canvas<'t: 'a, 'a: 's, 's, I, F, U: 's>(
    &mut self,
    textures: I,
    f: F
) -> Result<(), TargetRenderError>where
    for<'r> F: FnMut(&'r mut Canvas<T>, &U),
    I: Iterator<Item = &'s (&'a mut Texture<'t>, U)>,

Same as with_texture_canvas, but allows to change multiple Textures at once with the least amount of overhead. It means that between every iteration the Target is not reset to the source, and that the fact that the Canvas supports render target isn’t checked every iteration either; the check is actually only done once, at the beginning, avoiding useless checks.

The closure is run once for every Texture sent as parameter.

The main changes from with_texture_canvas is that is takes an Iterator of (&mut Texture, U), where U is a type defined by the user. The closure takes a &mut Canvas, and &U as arguments instead of a simple &mut Canvas. This user-defined type allows you to keep track of what to do with the Canvas you have received in the closure.

You will usually want to keep track of the number, a property, or anything that will allow you to uniquely track this Texture, but it can also be an empty struct or () as well!

Examples

Let’s create two textures, one which will be yellow, and the other will be white

let texture_creator = canvas.texture_creator();
enum TextureColor {
    Yellow,
    White,
};

let mut square_texture1 : Texture =
    texture_creator.create_texture_target(None, 100, 100).unwrap();
let mut square_texture2 : Texture =
    texture_creator.create_texture_target(None, 100, 100).unwrap();
let textures : Vec<(&mut Texture, TextureColor)> = vec![
    (&mut square_texture1, TextureColor::Yellow),
    (&mut square_texture2, TextureColor::White)
];
let result : Result<(), _> =
    canvas.with_multiple_texture_canvas(textures.iter(), |texture_canvas, user_context| {
    match *user_context {
        TextureColor::White => {
            texture_canvas.set_draw_color(Color::RGB(255, 255, 255));
        },
        TextureColor::Yellow => {
            texture_canvas.set_draw_color(Color::RGB(255, 255, 0));
        }
    };
    texture_canvas.clear();
});
// square_texture1 is now Yellow and square_texture2 is now White!

impl<T: RenderTarget> Canvas<T>

Drawing methods

pub fn raw(&self) -> *mut SDL_Renderer

pub fn set_draw_color<C: Into<Color>>(&mut self, color: C)

Sets the color used for drawing operations (Rect, Line and Clear).

pub fn draw_color(&self) -> Color

Gets the color used for drawing operations (Rect, Line and Clear).

pub fn set_blend_mode(&mut self, blend: BlendMode)

Sets the blend mode used for drawing operations (Fill and Line).

pub fn blend_mode(&self) -> BlendMode

Gets the blend mode used for drawing operations.

pub fn clear(&mut self)

Clears the current rendering target with the drawing color.

pub fn present(&mut self)

Updates the screen with any rendering performed since the previous call.

SDL’s rendering functions operate on a backbuffer; that is, calling a rendering function such as draw_line() does not directly put a line on the screen, but rather updates the backbuffer. As such, you compose your entire scene and present the composed backbuffer to the screen as a complete picture.

pub fn output_size(&self) -> Result<(u32, u32), String>

Gets the output size of a rendering context.

pub fn set_logical_size(
    &mut self,
    width: u32,
    height: u32
) -> Result<(), IntegerOrSdlError>

Sets a device independent resolution for rendering.

pub fn logical_size(&self) -> (u32, u32)

Gets device independent resolution for rendering.

pub fn set_viewport<R: Into<Option<Rect>>>(&mut self, rect: R)

Sets the drawing area for rendering on the current target.

pub fn viewport(&self) -> Rect

Gets the drawing area for the current target.

pub fn set_clip_rect<R: Into<Option<Rect>>>(&mut self, rect: R)

Sets the clip rectangle for rendering on the specified target.

If the rectangle is None, clipping will be disabled.

pub fn clip_rect(&self) -> Option<Rect>

Gets the clip rectangle for the current target.

Returns None if clipping is disabled.

pub fn set_scale(&mut self, scale_x: f32, scale_y: f32) -> Result<(), String>

Sets the drawing scale for rendering on the current target.

pub fn scale(&self) -> (f32, f32)

Gets the drawing scale for the current target.

pub fn draw_point<P: Into<Point>>(&mut self, point: P) -> Result<(), String>

Draws a point on the current rendering target. Errors if drawing fails for any reason (e.g. driver failure)

pub fn draw_points<'a, P: Into<&'a [Point]>>(
    &mut self,
    points: P
) -> Result<(), String>

Draws multiple points on the current rendering target. Errors if drawing fails for any reason (e.g. driver failure)

pub fn draw_line<P1: Into<Point>, P2: Into<Point>>(
    &mut self,
    start: P1,
    end: P2
) -> Result<(), String>

Draws a line on the current rendering target. Errors if drawing fails for any reason (e.g. driver failure)

pub fn draw_lines<'a, P: Into<&'a [Point]>>(
    &mut self,
    points: P
) -> Result<(), String>

Draws a series of connected lines on the current rendering target. Errors if drawing fails for any reason (e.g. driver failure)

pub fn draw_rect(&mut self, rect: Rect) -> Result<(), String>

Draws a rectangle on the current rendering target. Errors if drawing fails for any reason (e.g. driver failure)

pub fn draw_rects(&mut self, rects: &[Rect]) -> Result<(), String>

Draws some number of rectangles on the current rendering target. Errors if drawing fails for any reason (e.g. driver failure)

pub fn fill_rect<R: Into<Option<Rect>>>(&mut self, rect: R) -> Result<(), String>

Fills a rectangle on the current rendering target with the drawing color. Passing None will fill the entire rendering target. Errors if drawing fails for any reason (e.g. driver failure)

pub fn fill_rects(&mut self, rects: &[Rect]) -> Result<(), String>

Fills some number of rectangles on the current rendering target with the drawing color. Errors if drawing fails for any reason (e.g. driver failure)

pub fn copy<R1, R2>(
    &mut self,
    texture: &Texture<'_>,
    src: R1,
    dst: R2
) -> Result<(), String>where
    R1: Into<Option<Rect>>,
    R2: Into<Option<Rect>>,

Copies a portion of the texture to the current rendering target.

• If src is None, the entire texture is copied.
• If dst is None, the texture will be stretched to fill the given rectangle.

Errors if drawing fails for any reason (e.g. driver failure), or if the provided texture does not belong to the renderer.

pub fn copy_ex<R1, R2, P>(
    &mut self,
    texture: &Texture<'_>,
    src: R1,
    dst: R2,
    angle: f64,
    center: P,
    flip_horizontal: bool,
    flip_vertical: bool
) -> Result<(), String>where
    R1: Into<Option<Rect>>,
    R2: Into<Option<Rect>>,
    P: Into<Option<Point>>,

Copies a portion of the texture to the current rendering target, optionally rotating it by angle around the given center and also flipping it top-bottom and/or left-right.

• If src is None, the entire texture is copied.
• If dst is None, the texture will be stretched to fill the given rectangle.
• If center is None, rotation will be done around the center point of dst, or src if dst is None.

Errors if drawing fails for any reason (e.g. driver failure), if the provided texture does not belong to the renderer, or if the driver does not support RenderCopyEx.

pub fn read_pixels<R: Into<Option<Rect>>>(
    &self,
    rect: R,
    format: PixelFormatEnum
) -> Result<Vec<u8>, String>

Reads pixels from the current rendering target.

Remarks

WARNING: This is a very slow operation, and should not be used frequently.

Methods from Deref<Target = RendererContext<T::Context>>

pub fn info(&self) -> RendererInfo

Gets information about the rendering context.

pub fn raw(&self) -> *mut SDL_Renderer

Gets the raw pointer to the SDL_Renderer

Trait Implementations

impl<T: RenderTarget> Deref for Canvas<T>

type Target = RendererContext<<T as RenderTarget>::Context>

The resulting type after dereferencing.

fn deref(&self) -> &RendererContext<T::Context>

Dereferences the value.