DevTut

# Paint

A paint is one of the four objects needed to draw, along with a Canvas (holds drawing calls), a Bitmap (holds the pixels), and a drawing primitive (Rect, Path, Bitmap...)

# Creating a Paint

You can create a new paint with one of these 3 constructors:

  • new Paint() Create with default settings
  • new Paint(int flags) Create with flags
  • new Paint(Paint from) Copy settings from another paint

It is generally suggested to never create a paint object, or any other object in onDraw() as it can lead to performance issues. (Android Studio will probably warn you) Instead, make it global and initialize it in your class constructor like so:

public class CustomView extends View {
    
    private Paint paint;
    
    public CustomView(Context context) {
        super(context);
        paint = new Paint();
        //...
    }
    
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        paint.setColor(0xFF000000);
        // ...
    }
}

# Setting up Paint for text

# Text drawing settings

  • setTypeface(Typeface typeface) Set the font face. See Typeface (opens new window)
  • setTextSize(int size) Set the font size, in pixels.
  • setColor(int color) Set the paint drawing color, including the text color. You can also use setARGB(int a, int r, int g, int b and setAlpha(int alpha)
  • setLetterSpacing(float size) Set the spacing between characters, in ems. Default value is 0, a negative value will tighten the text, while a positive one will expand it.
  • setTextAlign(Paint.Align align) Set text alignment relative to its origin. Paint.Align.LEFT will draw it to the right of the origin, RIGHT will draw it to the left, and CENTER will draw it centered on the origin (horizontally)
  • setTextSkewX(float skewX) This could be considered as fake italic. SkewX represents the horizontal offset of the text bottom. (use -0.25 for italic)
  • setStyle(Paint.Style style) Fill text FILL, Stroke text STROKE, or both FILL_AND_STROKE

Note that you can use TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, size, getResources().getDisplayMetrics()) to convert from SP or DP to pixels.

# Measuring text

  • float width = paint.measureText(String text) Measure the width of text
  • float height = paint.ascent() Measure the height of text
  • paint.getTextBounds(String text, int start, int end, Rect bounds Stores the text dimensions. You have allocate the Rect, it cannot be null:

String text = "Hello world!";
 Rect bounds = new Rect();
 paint.getTextBounds(text, 0, text.length(), bounds);

There are other methods for measuring, however these three should fit most purposes.

# Setting up Paint for drawing shapes

  • setStyle(Paint.Style style) Filled shape FILL, Stroke shape STROKE, or both FILL_AND_STROKE
  • setColor(int color) Set the paint drawing color. You can also use setARGB(int a, int r, int g, int b and setAlpha(int alpha)
  • setStrokeCap(Paint.Cap cap) Set line caps, either ROUND, SQUARE, or BUTT (none) See this (opens new window).
  • setStrokeJoin(Paint.Join join) Set line joins, either MITER (pointy), ROUND, or BEVEL. See this (opens new window).
  • setStrokeMiter(float miter) Set miter join limit. This can prevent miter join from going on indefinitively, turning it into a bevel join after x pixels. See this (opens new window).
  • setStrokeWidth(float width) Set stroke width. 0 will draw in hairline mode, independant of the canvas matrix. (always 1 pixel)

# Setting flags

You can set the following flags in the constructor, or with setFlags(int flags)

  • Paint.ANTI_ALIAS_FLAG Enable antialiasing, smooths the drawing.
  • Paint.DITHER_FLAG Enable dithering. If color precision is higher than the device's, this will happen (opens new window).
  • Paint.EMBEDDED_BITMAP_TEXT_FLAG Enables the use of bitmap fonts.
  • Paint.FAKE_BOLD_TEXT_FLAG will draw text with a fake bold effect, can be used instead of using a bold typeface. Some fonts have styled bold, fake bold won't (opens new window)
  • Paint.FILTER_BITMAP_FLAG Affects the sampling of bitmaps when transformed.
  • Paint.HINTING_OFF, Paint.HINTING_ON Toggles font hinting, see this (opens new window)
  • Paint.LINEAR_TEXT_FLAG Disables font scaling, draw operations are scaled instead
  • Paint.SUBPIXEL_TEXT_FLAG Text will be computed using subpixel accuracy.
  • Paint.STRIKE_THRU_TEXT_FLAG Text drawn will be striked
  • Paint.UNDERLINE_TEXT_FLAG Text drawn will be underlined

You can add a flag and remove flags like this:

Paint paint = new Paint();
paint.setFlags(paint.getFlags() | Paint.FLAG);   // Add flag
paint.setFlags(paint.getFlags() & ~Paint.FLAG);  // Remove flag

Trying to remove a flag that isn't there or adding a flag that is already there won't change anything. Also note that most flags can also be set using set<Flag>(boolean enabled), for example setAntialias(true).

You can use paint.reset() to reset the paint to its default settings. The only default flag is EMBEDDED_BITMAP_TEXT_FLAG. It will be set even if you use new Paint(0), you will have

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