[Wayland] Weston multi screen display

Weston Multi screen display

• Weston Multi screen display is supported by default （ For example, front screen + Rear screen ）
  
• output An object can be understood as a logical screen , about DRM, Its information is via drmModeGetResources Interface to get .
• View There are two members in the structure to Record output Information , A preservation output Object as primary output, One is used to record the current View According to the output Information .

struct weston_view {
    
	//  Omit 
	/* * The primary output for this view. * Used for picking the output for driving internal animations on the * view, inheriting the primary output for related views in shells, etc. */
	struct weston_output *output;

	/* * A more complete representation of all outputs this surface is * displayed on. */
	uint32_t output_mask;
}

• weston_view_assign_output Function is responsible for view Distribute output object .

static void
weston_view_assign_output(struct weston_view *ev)
{
    
	struct weston_compositor *ec = ev->surface->compositor;
	struct weston_output *output, *new_output;
	pixman_region32_t region;
	uint32_t max, area, mask;
	pixman_box32_t *e;

	new_output = NULL;
	max = 0;
	mask = 0;
	pixman_region32_init(&region);
	wl_list_for_each(output, &ec->output_list, link) {
    
		if (output->destroying)
			continue;

		pixman_region32_intersect(&region, &ev->transform.boundingbox,
					  &output->region);

		e = pixman_region32_extents(&region);
		area = (e->x2 - e->x1) * (e->y2 - e->y1);
		
		//  Calculation mask
		if (area > 0)
			mask |= 1u << output->id;
		//  choice output
		if (area >= max) {
    
			new_output = output;
			max = area;
		}
	}
	pixman_region32_fini(&region);
	//  Distribute output
	ev->output = new_output;
	//  Record mask
	ev->output_mask = mask;

	weston_surface_assign_output(ev->surface);
}

• Process according to the above code , Select... For the largest display area output, As primary output. When there are two output（ Two screens ） According to the information in the figure above ,mask The processing is as follows

1. output0 Of id by 0, 1 Move left 0 position , obtain 1. Then with 0 do | operation . Final mask by 0001( Binary system ）
2. output1 Of id by 1,1 Move left 1 position , wait until 2. Then with 0001 do | function . Final mask by 0011（ Binary system ）.
3. Empathy , If there are four output, that mask The value of is 1111（ Binary system ）.

• Processing of the composite part ： About multi screen compositing , In fact, the single screen is mostly the same . Just a little more , To show output The judgment of the .
• weston_surface_schedule_repaint: Redraw operation ,surface commit and surface damage Will trigger this function .

/** * \param surface The surface to be repainted * * Marks the output(s) that the surface is shown on as needing to be * repainted. See weston_output_schedule_repaint(). */
WL_EXPORT void
weston_surface_schedule_repaint(struct weston_surface *surface)
{
    
	struct weston_output *output;
	wl_list_for_each(output, &surface->compositor->output_list, link)
		//  such as  output->id  by  0 output_mask by  0001
		//  Below   Judge , Would pass . This triggers the selected output Conduct repaint
		if (surface->output_mask & (1u << output->id))
			weston_output_schedule_repaint(output);
}