Proprietà HTML canvas globalCompositeOperation
Esempio
Disegna rettangoli usando due diversi valori di globalCompositeOperation. I rettangoli rossi sono immagini di destinazione . I rettangoli blu sono immagini di origine :
fonte finita
destinazione finita
JavaScript:
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.fillStyle = "red";
ctx.fillRect(20, 20, 75, 50);
ctx.globalCompositeOperation = "source-over";
ctx.fillStyle = "blue";
ctx.fillRect(50, 50, 75, 50);
ctx.fillStyle = "red";
ctx.fillRect(150, 20, 75, 50);
ctx.globalCompositeOperation = "destination-over";
ctx.fillStyle = "blue";
ctx.fillRect(180, 50, 75, 50);
Supporto del browser
Internet Explorer 9, Firefox, Opera, Chrome e Safari supportano la proprietà globalCompositeOperation.
Definizione e utilizzo
La proprietà globalCompositeOperation imposta o restituisce il modo in cui un'immagine di origine (nuova) viene disegnata su un'immagine di destinazione (esistente).
immagine sorgente = disegni che stai per posizionare sulla tela.
immagine di destinazione = disegni che sono già posizionati sulla tela.
| Valore di default: | fonte finita |
|---|---|
| sintassi JavaScript: | contesto .globalCompositeOperation="source-in"; |
Valori di proprietà
| Value | Description | Play it |
|---|---|---|
| source-over | Default. Displays the source image over the destination image | |
| source-atop | Displays the source image on top of the destination image. The part of the source image that is outside the destination image is not shown | |
| source-in | Displays the source image in to the destination image. Only the part of the source image that is INSIDE the destination image is shown, and the destination image is transparent | |
| source-out | Displays the source image out of the destination image. Only the part of the source image that is OUTSIDE the destination image is shown, and the destination image is transparent | |
| destination-over | Displays the destination image over the source image | |
| destination-atop | Displays the destination image on top of the source image. The part of the destination image that is outside the source image is not shown | |
| destination-in | Displays the destination image in to the source image. Only the part of the destination image that is INSIDE the source image is shown, and the source image is transparent | |
| destination-out | Displays the destination image out of the source image. Only the part of the destination image that is OUTSIDE the source image is shown, and the source image is transparent | |
| lighter | Displays the source image + the destination image | |
| copy | Displays the source image. The destination image is ignored | |
| xor | The source image is combined by using an exclusive OR with the destination image |
Esempio
Tutti i valori della proprietà globalCompositeOperation: