Unit -04 Drawing on the Screen

Lesson Plan: Unit - 04
Subject: P15A2AAD - Android Application Development
Topic of Study: Drawing on the Screen
Grade/Level: Master of Computer Applications
Objective: To demonstrate the different drawing on screen using java programming
Time Allotment: 55 Minutes

• Drawing on the Screen
• With Android, we can display images such as PNG and JPG graphics, as well as text and primitive shapes to the screen.
• We can paint these items with various colors, styles, or gradients and modify them using standard image transforms.
• We can even animate objects to give the illusion of motion.
• Output:
• Exa.
  
• Step 01: Write a class (DotCircle.java)
• Exa.
  
• Step 02: Call DotCircle.java into MainActivity.java.
• Exa.
  
• Understanding the Canvas:
• The Canvas (android.graphics.Canvas) object holds the draw calls, in order, for a rectangle of space.
• There are methods available for drawing images, text, shapes, and support for clipping regions.
• The dimensions of the Canvas are bound by the container view.
• You can retrieve the size of the Canvas using the getHeight() and getWidth() methods.
• Understanding the Paint:
• In Android, the Paint (android.graphics.Paint) object stores far more than a color.
• The Paint class encapsulates the style and complex color and rendering information, which can be applied to a drawable like a graphic, shape, or piece of text in a given Typeface.
• In Android, the Paint (android.graphics.Paint) object stores far more than a color.
• The Paint class encapsulates the style and complex color and rendering information,which can be applied to a drawable like a graphic, shape, or piece of text in a given Typeface.
• Working with Paint Color:
• You can set the color of the Paint using the setColor() method.
• Standard colors are predefined within the android.graphics.Color class. 
• Exa.
• To sets the paint color to red: 

                                       Paint redPaint =  new Paint();

                                      redPaint.setColor(Color.RED);

• Working with Paint Antialiasing:
• Antialiasing makes many graphics—whether they are shapes or typefaces—look smootheron the screen.
• This property is set within the Paint of an object.
• Exa.
• Paint object with antialiasing enabled:

                                  Paint aliasedPaint =  new Paint(Paint.ANTI_ALIAS_FLAG);

• Working with Paint Styles:
• Paint style controls how an object is filled with color. 
• Exa.
• Paint object and sets the Style to STROKE, which signifies that the object should be painted as a line drawing and not filled (the default):

                                      Paint linePaint= new Paint();

                                      linePaint.setStyle(Paint.Style.STROKE);

Working with Paint Gradients:

• You can create a gradient of colors using one of the gradient subclasses.
• The different gradient classes, including LinearGradient, RadialGradient, and SweepGradient, are available under the superclass android.graphics.Shader.
• All gradients need at least two colors—a start color and an end color—but might contain any number of colors in an array.
• The different types of gradients are differentiated by the direction in which the gradient “flows.” 
• Gradients can be set to mirror and repeat as necessary.
• You can set the Paint gradient using the setShader() method.
• Working with Linear Gradients:
• A linear gradient is one that changes colors along a single straight line.
• The top-left circle is a linear gradient between yellow and red, which is mirrored.
• You can achieve this by creating a LinearGradient and setting the Paint method setShader() before drawing on a Canvas, as follows:
• exa. 
  
• Working with Radial Gradients:
• A radial gradient is one that changes colors starting at a single point and radiating outward in a circle.
• The smaller circle on the right is a radial gradient between green and black.
• You can achieve this by creating a RadialGradient and setting the Paint method setShader() before drawing on a Canvas, as follows:
• exa.
  
• Working with Sweep Gradients
• A sweep gradient is one that changes colors using slices of a pie.
• This type of gradient is often used for a color chooser.
• The large circle at the bottom is a sweep gradient between red, yellow, green, blue, and magenta.
• You can achieve this by creating a SweepGradient and setting the Paint method setShader() before drawing on a Canvas, as follows:
• exa.