Chromium Code Reviews
chromiumcodereview-hr@appspot.gserviceaccount.com (chromiumcodereview-hr) | Please choose your nickname with Settings | Help | Chromium Project | Gerrit Changes | Sign out
(8)

Unified Diff: site/user/api/skcanvas.md

Issue 1127383010: Documentation: SkCanvas API (Closed) Base URL: https://skia.googlesource.com/skia.git@master
Patch Set: 2015-05-19 (Tuesday) 13:19:57 EDT Created 5 years, 7 months ago
Use n/p to move between diff chunks; N/P to move between comments. Draft comments are only viewable by you.
Jump to:
View side-by-side diff with in-line comments
Download patch
« no previous file with comments | « site/user/api/index.md ('k') | site/user/api/skmatrix.md » ('j') | no next file with comments »
Expand Comments ('e') | Collapse Comments ('c') | Show Comments Hide Comments ('s')
Index: site/user/api/skcanvas.md
diff --git a/site/user/api/skcanvas.md b/site/user/api/skcanvas.md
new file mode 100644
index 0000000000000000000000000000000000000000..157409da3863f438516d39ad59b76ade36313a32
--- /dev/null
+++ b/site/user/api/skcanvas.md
@@ -0,0 +1,132 @@
+SkCanvas
+========
+
+*The drawing context*
+
+<!-- Updated Mar 4, 2011 -->
+
+Preview
+-------
+
+Here is an example of a set of drawing commands to draw a filled
+heptagram. This function can be cut and pasted into
+[fiddle.skia.org](https://fiddle.skia.org/).
+
+<!--?prettify lang=cc?-->
+
+ void draw(SkCanvas* canvas) {
+ const SkScalar scale = 256.0f;
+ const SkScalar R = 0.45f * scale;
+ const SkScalar TAU = 6.2831853f;
+ SkPath path;
+ for (int i = 0; i < 7; ++i) {
+ SkScalar theta = 3 * i * TAU / 7;
+ if (i == 0) {
+ path.moveTo(R * cos(theta), R * sin(theta));
+ } else {
+ path.lineTo(R * cos(theta), R * sin(theta));
+ }
+ }
+ path.close();
+ SkPaint p;
+ p.setAntiAlias(true);
+ canvas->clear(SK_ColorWHITE);
+ canvas->translate(0.5f * scale, 0.5f * scale);
+ canvas->drawPath(path, p);
+ }
+
+Details
+-------
+
+SkCanvas is the drawing context for Skia. It knows where to direct the
+drawing (i.e. where the screen of offscreen pixels are), and maintains
+a stack of matrices and clips. Note however, that unlike similar
+contexts in other APIs like postscript, cairo, or awt, Skia does not
+store any other drawing attributes in the context (e.g. color, pen
+size). Rather, these are specified explicitly in each draw call, via a
+SkPaint.
+
+<!--?prettify lang=cc?-->
+
+ void draw(SkCanvas* canvas) {
+ canvas->save();
+ canvas->rotate(SkIntToScalar(45));
+ SkRect rect = SkRect::MakeXYWH(150, -50, 100, 100);
+ SkPaint paint;
+ canvas->drawRect(rect, paint);
+ canvas->restore();
+ }
+
+The code above will draw a rectangle rotated by 45 degrees. Exactly
+what color and style the rect will be drawn in is described by the
+paint, not the canvas.
+
+Check out more detailed info on [creating a SkCanvas object](canvas).
+
+To begin with, we might want to erase the entire canvas. We can do
+this by drawing an enormous rectangle, but there are easier ways to do
+it.
+
+<!--?prettify lang=cc?-->
+
+ void draw(SkCanvas* canvas) {
+ SkPaint paint;
+ paint.setColor(SK_ColorWHITE);
+ canvas->drawPaint(paint);
+ }
+
+This fills the entire canvas (though respecting the current clip of
+course) with whatever color or shader (and xfermode) is specified by
+the paint. If there is a shader in the paint, then it will respect the
+current matrix on the canvas as well (see SkShader). If you just want
+to draw a color (with an optional xfermode), you can just call
+drawColor(), and save yourself having to allocate a paint.
+
+<!--?prettify lang=cc?-->
+
+ void draw(SkCanvas* canvas) {
+ canvas->drawColor(SK_ColorWHITE);
+ }
+
+All of the other draw APIs are similar, each one ending with a paint
+parameter.
+
+<!--?prettify lang=cc?-->
+
+ void draw(SkCanvas* canvas) {
+ SkPaint paint;
+ paint.setStyle(SkPaint::kStroke_Style);
+ paint.setStrokeWidth(2);
+
+ SkRect rect = SkRect::MakeXYWH(50, 50, 40, 60);
+ canvas->drawRect(rect, paint);
+
+ SkRRect oval;
+ oval.setOval(rect);
+ oval.offset(40, 60);
+ canvas->drawRRect(oval, paint);
+
+ canvas->drawCircle(180, 50, 25, paint);
+
+ rect.offset(80, 0);
+ canvas->drawRoundRect(rect, 10, 10, paint);
+
+ SkPath path;
+ path.cubicTo(768, 0, -512, 256, 256, 256);
+ canvas->drawPath(path, paint);
+
+ canvas->drawBitmap(source, 128, 128, &paint);
+
+ SkRect rect2 = SkRect::MakeXYWH(0, 0, 40, 60);
+ canvas->drawBitmapRect(source, rect2);
+
+ SkPaint paint2;
+ const char text[] = "Hello, Skia!";
+ canvas->drawText(text, strlen(text), 50, 25, paint2);
+ }
+
+In some of the calls, we pass a pointer, rather than a reference, to
+the paint. In those instances, the paint parameter may be null. In all
+other cases the paint parameter is required.
+
+Next: [SkPaint](/user/api/skpaint)
« no previous file with comments | « site/user/api/index.md ('k') | site/user/api/skmatrix.md » ('j') | no next file with comments »

Powered by Google App Engine
This is Rietveld 408576698