1.165 class sdl_texture

An sdl_texture holds pixels that the SDL renderer draws itself, without Cairo. An sdl_layer places it in an sdl_window or sdl_canvas, or maps it onto the triangles of an sdl_mesh. The pixels keep the format they arrived in: camera->texture stores the frames of a camera in, e.g., YUY2, and the renderer converts them to RGB when it draws them, on the GPU if it can. This makes it suitable for video.

Copying the pixels from and to an image is cheap for pixels in ARGB: these are stored with premultiplied alpha, as Cairo stores them.

The renderer of each frame that shows the texture keeps its own copy. After the pixels change, these copies are updated and the frames are drawn again; the Cairo drawings of the windows are not redrawn.

new(T, sdl_texture(image('pce.png'))),
new(W, sdl_window),
send(W, append, sdl_layer(T)),
send(W, open).

See also

- class sdl_layer
- class sdl_window
- class sdl_mesh
- camera<->texture

1.165.1 Instance variables

sdl_texture <- hot_spot: point*

Point of the texture, in its pixels, that is placed at the position of an sdl_layer using scale none and around which the layer rotates. @nil places the top-left corner and rotates around the centre. Copied from the image or set to the origin of the graphical the texture is made from.

1.165.2 Send methods

sdl_texture ->initialise: from=[image|size|graphical]

Create with a copy of the pixels of an image or, given a size, with transparent pixels. Given a graphical, the texture is as large as its bounding box, including room for, e.g., a glow, and holds the graphical drawn with Cairo. If the origin of the graphical, the point (0,0) of its coordinates, is on the texture, it becomes sdl_texture<-hot_spot: a figure drawn around its origin thus becomes a sprite that rotates around that point. Without an argument the texture has no pixels until, e.g., a camera delivers a frame.

sdl_texture ->image: image

Replace the pixels by a copy of those of the image. The size changes to the size of the image.

sdl_texture ->draw_in: graphical, at=[point]

Paint the graphical onto the pixels using Cairo, at the given position or else at its own position. As image->draw_in. Pixels in another format than ARGB, such as a camera frame, are first converted to ARGB. The texture is shown again where it is displayed.

sdl_texture ->changed:

Show the pixels again wherever the texture is displayed. This is done by the methods that change the pixels.

1.165.3 Get methods

sdl_texture <-image: -> image

New image holding a copy of the pixels, converted to RGB. Use this to save or analyse a frame of a camera. image->copy copies the pixels into an existing image.

sdl_texture <-size: -> size

New size object holding the size in pixels. size(0,0) if there are no pixels.

sdl_texture <-format: -> name*

Name of the pixel format, e.g., argb8888 or the yuy2 and nv12 of cameras. @nil if there are no pixels.