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const RenderData = struct {
output: *c.wlr_output,
renderer: *c.wlr_renderer,
view: *View,
when: *c.struct_timespec,
};
fn render_surface(surface: [*c]c.wlr_surface, sx: c_int, sy: c_int, data: ?*c_void) callconv(.C) void {
// This function is called for every surface that needs to be rendered.
var rdata = @ptrCast(*RenderData, @alignCast(@alignOf(RenderData), data));
var view = rdata.*.view;
var output = rdata.*.output;
// We first obtain a wlr_texture, which is a GPU resource. wlroots
// automatically handles negotiating these with the client. The underlying
// resource could be an opaque handle passed from the client, or the client
// could have sent a pixel buffer which we copied to the GPU, or a few other
// means. You don't have to worry about this, wlroots takes care of it.
var texture = c.wlr_surface_get_texture(surface);
if (texture == null) {
return;
}
// The view has a position in layout coordinates. If you have two displays,
// one next to the other, both 1080p, a view on the rightmost display might
// have layout coordinates of 2000,100. We need to translate that to
// output-local coordinates, or (2000 - 1920).
var ox: f64 = 0.0;
var oy: f64 = 0.0;
c.wlr_output_layout_output_coords(view.*.server.*.output_layout, output, &ox, &oy);
ox += @intToFloat(f64, view.*.x + sx);
oy += @intToFloat(f64, view.*.y + sy);
// We also have to apply the scale factor for HiDPI outputs. This is only
// part of the puzzle, TinyWL does not fully support HiDPI.
var box = c.wlr_box{
.x = @floatToInt(c_int, ox * output.*.scale),
.y = @floatToInt(c_int, oy * output.*.scale),
.width = @floatToInt(c_int, @intToFloat(f32, surface.*.current.width) * output.*.scale),
.height = @floatToInt(c_int, @intToFloat(f32, surface.*.current.height) * output.*.scale),
};
// Those familiar with OpenGL are also familiar with the role of matricies
// in graphics programming. We need to prepare a matrix to render the view
// with. wlr_matrix_project_box is a helper which takes a box with a desired
// x, y coordinates, width and height, and an output geometry, then
// prepares an orthographic projection and multiplies the necessary
// transforms to produce a model-view-projection matrix.
//
// Naturally you can do this any way you like, for example to make a 3D
// compositor.
var matrix: [9]f32 = undefined;
var transform = c.wlr_output_transform_invert(surface.*.current.transform);
c.wlr_matrix_project_box(&matrix, &box, transform, 0.0, &output.*.transform_matrix);
// This takes our matrix, the texture, and an alpha, and performs the actual
// rendering on the GPU.
_ = c.wlr_render_texture_with_matrix(rdata.*.renderer, texture, &matrix, 1.0);
// This lets the client know that we've displayed that frame and it can
// prepare another one now if it likes.
c.wlr_surface_send_frame_done(surface, rdata.*.when);
}
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