Chromium Code Reviews
chromiumcodereview-hr@appspot.gserviceaccount.com (chromiumcodereview-hr) | Please choose your nickname with Settings | Help | Chromium Project | Gerrit Changes | Sign out
(2)

Unified Diff: site/user/api/skpaint.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/skmatrix.md ('k') | site/user/api/skrect.md » ('j') | no next file with comments »
Expand Comments ('e') | Collapse Comments ('c') | Show Comments Hide Comments ('s')
Index: site/user/api/skpaint.md
diff --git a/site/user/api/skpaint.md b/site/user/api/skpaint.md
new file mode 100644
index 0000000000000000000000000000000000000000..fdee783d4b992aa82cf5fb17968124a1f82d7a95
--- /dev/null
+++ b/site/user/api/skpaint.md
@@ -0,0 +1,102 @@
+SkPaint
+=======
+
+*color, stroke, font, effects*
+
+<!-- Updated Jan 17, 2013 by humper@google.com -->
+
+Anytime you draw something in Skia, and want to specify what color it
+is, or how it blends with the background, or what style or font to
+draw it in, you specify those attributes in a paint.
+
+Unlike `SkCanvas`, paints do not maintain an internal stack of state
+(i.e. there is no save/restore on a paint). However, paints are
+relatively light-weight, so the client may create and maintain any
+number of paint objects, each setup for a particular use. Factoring
+all of these color and stylistic attribute out of the canvas state,
+and into (multiple) paint objects, allows canvas' save/restore to be
+that much more efficient, as all they have to do is maintain the stack
+of matrix and clip settings.
+
+<!--?prettify lang=cc?-->
+
+ SkPaint paint1, paint2, paint3;
+
+ paint1.setColor(0xFFFF0000:
+ paint1.setStyle(SkPaint::kFill_Style);
+
+ paint2.setColor(0x8000FF00);
+ paint2.setStyle(SkPaint::kStroke_Style);
+ paint2.setStrokeWidth(SkIntToScalar(3));
+
+ paint3.setColor(0xFF888888);
+ paint3.setTextSize(SkIntToScalar(24));
+ paint3.setTextScaleX(SkFloatToScalar(0.75f));
+
+
+This shows three different paints, each setup to draw in a different
+style. Now the caller can intermix these paints freely, either using
+them as is, or modifying them as the drawing proceeds.
+
+<!--?prettify lang=cc?-->
+
+ canvas->drawRect(..., paint1);
+ canvas->drawRect(..., paint2);
+
+ paint2.setStrokeWidth(SkIntToScalar(5));
+ canvas->drawOval(..., paint2);
+
+ canvas->drawText(..., paint3);
+ paint3.setColor(0xFF0000FF);
+ canvas->drawText(..., paint3);
+
+
+Beyond simple attributes such as color, strokes, and text values,
+paints support effects. These are subclasses of different aspects of
+the drawing pipeline, that when referenced by a paint (each of them is
+reference-counted), are called to override some part of the drawing
+pipeline.
+
+For example, to draw using a gradient instead of a single color,
+assign a SkShader to the paint.
+
+<!--?prettify lang=cc?-->
+
+ SkShader* shader = SkGradientShader::CreateLinear(...);
+ paint.setShader(shader);
+ shader->unref();
+
+Now, anything drawn with that paint will be drawn with the gradient
+specified in the call to CreateLinear(). The shader object that is
+returned is reference-counted. Whenever any effects object, like a
+shader, is assigned to a paint, its reference-count is increased by
+the paint. To balance this, the caller in the above example calls
+unref() on the shader once it has assigned it to the paint. Now the
+paint is the only "owner" of that shader, and it will automatically
+call unref() on the shader when either the paint goes out of scope, or
+if another shader (or null) is assigned to it.
+
+There are 6 types of effects that can be assigned to a paint:
+
+* **SkPathEffect** - modifications to the geometry (path) before it
+ generates an alpha mask (e.g. dashing)
+* **SkRasterizer** - composing custom mask layers (e.g. shadows)
+* **SkMaskFilter** - modifications to the alpha mask before it is
+ colorized and drawn (e.g. blur, emboss)
+* **SkShader** - e.g. gradients (linear, radial, sweep), bitmap patterns
+ (clamp, repeat, mirror)
+* **SkColorFilter** - modify the source color(s) before applying the
+ xfermode (e.g. color matrix)
+* **SkXfermode** - e.g. porter-duff transfermodes, blend modes
+
+Paints also hold a reference to a SkTypeface. The typeface represents
+a specific font style, to be used for measuring and drawing
+text. Speaking of which, paints are used not only for drawing text,
+but also for measuring it.
+
+<!--?prettify lang=cc?-->
+
+ paint.measureText(...);
+ paint.getTextBounds(...);
+ paint.textToGlyphs(...);
+ paint.getFontMetrics(...);
« no previous file with comments | « site/user/api/skmatrix.md ('k') | site/user/api/skrect.md » ('j') | no next file with comments »

Powered by Google App Engine
This is Rietveld 408576698