1--- 2title: 'SkPaint Overview' 3linkTitle: 'SkPaint Overview' 4 5weight: 280 6--- 7 8Anytime you draw something in Skia, and want to specify what color it is, or how 9it blends with the background, or what style or font to draw it in, you specify 10those attributes in a paint. 11 12Unlike `SkCanvas`, paints do not maintain an internal stack of state (i.e. there 13is no save/restore on a paint). However, paints are relatively light-weight, so 14the client may create and maintain any number of paint objects, each set up for 15a particular use. Factoring all of these color and stylistic attributes out of 16the canvas state, and into (multiple) paint objects, allows canvas' save/restore 17to be that much more efficient, as all they have to do is maintain the stack of 18matrix and clip settings. 19 20<fiddle-embed-sk name='@skpaint_skia'></fiddle-embed-sk> 21 22This shows three different paints, each set up to draw in a different style. Now 23the caller can intermix these paints freely, either using them as is, or 24modifying them as the drawing proceeds. 25 26<fiddle-embed-sk name='@skpaint_mix'></fiddle-embed-sk> 27 28Beyond simple attributes such as color, strokes, and text values, paints support 29effects. These are subclasses of different aspects of the drawing pipeline, that 30when referenced by a paint (each of them is reference-counted), are called to 31override some part of the drawing pipeline. 32 33For example, to draw using a gradient instead of a single color, assign a 34SkShader to the paint. 35 36<fiddle-embed-sk name='@skpaint_shader'></fiddle-embed-sk> 37 38Now, anything drawn with that paint will be drawn with the gradient specified in 39the call to `MakeLinear()`. The shader object that is returned is 40reference-counted. Whenever any effects object, like a shader, is assigned to a 41paint, its reference-count is increased by the paint. To balance this, the 42caller in the above example calls `unref()` on the shader once it has assigned 43it to the paint. Now the paint is the only "owner" of that shader, and it will 44automatically call `unref()` on the shader when either the paint goes out of 45scope, or if another shader (or null) is assigned to it. 46 47There are 6 types of effects that can be assigned to a paint: 48 49- **SkPathEffect** - modifications to the geometry (path) before it generates an 50 alpha mask (e.g. dashing) 51- **SkRasterizer** - composing custom mask layers (e.g. shadows) 52- **SkMaskFilter** - modifications to the alpha mask before it is colorized and 53 drawn (e.g. blur) 54- **SkShader** - e.g. gradients (linear, radial, sweep), bitmap patterns (clamp, 55 repeat, mirror) 56- **SkColorFilter** - modify the source color(s) before applying the blend 57 (e.g. color matrix) 58- **SkBlendMode** - e.g. porter-duff transfermodes, blend modes 59 60Paints also hold a reference to a SkTypeface. The typeface represents a specific 61font style, to be used for measuring and drawing text. Speaking of which, paints 62are used not only for drawing text, but also for measuring it. 63 64<!--?prettify lang=cc?--> 65 66 paint.measureText(...); 67 paint.getTextBounds(...); 68 paint.textToGlyphs(...); 69 paint.getFontMetrics(...); 70 71## SkBlendMode 72 73The following example demonstrates all of the Skia's standard blend modes. In 74this example the source is a solid magenta color with a horizontal alpha 75gradient and the destination is a solid cyan color with a vertical alpha 76gradient. 77 78<fiddle-embed-sk name='@skpaint_xfer'></fiddle-embed-sk> 79 80## SkShader 81 82Several shaders are defined (besides the linear gradient already mentioned): 83 84- Bitmap Shader 85 86 <fiddle-embed-sk name='@skpaint_bitmap_shader'></fiddle-embed-sk> 87 88- Radial Gradient Shader 89 90 <fiddle-embed-sk name='@skpaint_radial'></fiddle-embed-sk> 91 92- Two-Point Conical Gradient Shader 93 94 <fiddle-embed-sk name='@skpaint_2pt'></fiddle-embed-sk> 95 96- Sweep Gradient Shader 97 98 <fiddle-embed-sk name='@skpaint_sweep'></fiddle-embed-sk> 99 100- Fractal Perlin Noise Shader 101 102 <fiddle-embed-sk name='@skpaint_perlin'></fiddle-embed-sk> 103 104- Turbulence Perlin Noise Shader 105 106 <fiddle-embed-sk name='@skpaint_turb'></fiddle-embed-sk> 107 108- Compose Shader 109 110 <fiddle-embed-sk name='@skpaint_compose_shader'></fiddle-embed-sk> 111 112## SkMaskFilter 113 114- Blur Mask Filter 115 116 <fiddle-embed-sk name='@skpaint_blur_mask_filter'></fiddle-embed-sk> 117 118## SkColorFilter 119 120- Color Matrix Color Filter 121 122 <fiddle-embed-sk name='@skpaint_matrix_color_filter'></fiddle-embed-sk> 123 124- Color Table Color Filter 125 126 <fiddle-embed-sk name='@skpaint_color_table_filter'></fiddle-embed-sk> 127 128## SkPathEffect 129 130- SkPath2DPathEffect: Stamp the specified path to fill the shape, using the 131 matrix to define the latice. 132 133 <fiddle-embed-sk name='@skpaint_path_2d_path_effect'></fiddle-embed-sk> 134 135- SkLine2DPathEffect: a special case of SkPath2DPathEffect where the path is a 136 straight line to be stroked, not a path to be filled. 137 138 <fiddle-embed-sk name='@skpaint_line_2d_path_effect'></fiddle-embed-sk> 139 140- SkPath1DPathEffect: create dash-like effects by replicating the specified path 141 along the drawn path. 142 143 <fiddle-embed-sk name='@skpaint_path_1d_path_effect'></fiddle-embed-sk> 144 145- SkCornerPathEffect: a path effect that can turn sharp corners into various 146 treatments (e.g. rounded corners). 147 148 <fiddle-embed-sk name='@skpaint_corner_path_effects'></fiddle-embed-sk> 149 150- SkDashPathEffect: a path effect that implements dashing. 151 152 <fiddle-embed-sk name='@skpaint_dash_path_effect'></fiddle-embed-sk> 153 154- SkDiscretePathEffect: This path effect chops a path into discrete segments, 155 and randomly displaces them. 156 157 <fiddle-embed-sk name='@skpaint_discrete_path_effect'></fiddle-embed-sk> 158 159- SkComposePathEffect: a pathEffect whose effect is to apply first the inner 160 pathEffect and the the outer pathEffect (i.e. outer(inner(path))). 161 162 <fiddle-embed-sk name='@skpaint_compose_path_effect'></fiddle-embed-sk> 163 164- SkSumPathEffect: a pathEffect whose effect is to apply two effects, in 165 sequence (i.e. first(path) + second(path)). 166 167 <fiddle-embed-sk name='@skpaint_sum_path_effect'></fiddle-embed-sk> 168