83 lines
2.0 KiB
Markdown
83 lines
2.0 KiB
Markdown
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```go
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```go
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type Area struct { // implements Control
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// Paint receives requests to redraw from the window system.
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Paint chan PaintRequest
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// Keyboard receives keyboard events.
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Key chan KeyEvent // not covered here
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// Mouse receives mouse events.
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Mouse chan MouseEvent // not covered here
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}
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// PaintRequest represents a request to redraw an Area.
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// It is sent across Area.Paint.
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type PaintRequest struct {
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// Rect is the clipping rectangle that needs redraw.
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Rect image.Rect
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// Out is a channel on which you send the image to redraw.
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Out chan<- *image.NRGBA
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}
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```
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and an example of intended use:
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```go
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func myAreaGoroutine(area *ui.Area, start <-chan bool) {
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var img *image.NRGBA
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// initialize img here
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<-start // sent after calling Window.Open()
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area.SetSize(img.Rect.Dx(), img.Rect.Dy()) // sets the internal size; scrollbars and scrolling is handled automatically
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for {
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select {
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case req := <-area.Paint:
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req.Out <- img.SubImage(req.Rect).(*image.NRGBA)
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case e := <-area.Mouse:
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// draw on a mouse click, for instance
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}
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}
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}
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```
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## Windows
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TODO
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## GTK+
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We can use `GtkDrawingArea`. We hook into the `draw` signal; it does something equivalent to
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```go
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func draw_callback(widget *C.GtkWidget, cr *C.cairo_t, data C.gpointer) C.gboolean {
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s := (*sysData)(unsafe.Pointer(data))
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// TODO get clip rectangle that needs drawing
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imgret := make(chan *image.NRGBA)
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defer close(imgret)
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s.paint <- PaintRequest{
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Rect: /* clip rect */,
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Out: imgret,
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}
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i := <-imgret
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pixbuf := C.gdk_pixbuf_new_from_data(
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(*C.guchar)(unsafe.Pointer(&i.Pix[0])),
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C.GDK_COLORSPACE_RGB,
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C.TRUE, // has alpha channel
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8, // bits per sample
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C.int(i.Rect.Dx()),
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C.int(i.Rect.Dy()),
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C.int(i.Stride),
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nil, nil) // do not free data
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C.gdk_cairo_set_source_pixbuf(cr,
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pixbuf,
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/* x of clip rect */,
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/* y of clip rect */)
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return C.FALSE // TODO what does this return value mean? docs don't say
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}
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```
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TODO figure out how scrolling plays into this
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## Cocoa
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TODO
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