Create CONTRIBUTING.md

Author: anastr

CONTRIBUTING.md

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+if you want to contribute to this library, _Please_ take look at these **rules**.
+
+_**First:**_ you must read [Get Starting](https://github.com/anastr/SpeedView/wiki/0.-Get-Started) and [Advanced Usage](https://github.com/anastr/SpeedView/wiki/Usage).
+
+before you start, you have to know what you want to do:
+ * [Fix Bugs](#fix-bugs).
+ * [improve the Library](#improve-the-Library).
+ * [Create New Speedometer](#create-new-speedometer).
+ * [Build New Component](#build-new-component).
+
+## Fix Bugs
+report abut the bug with explain and Screenshots _if it possible_, and we will discuss about it to solve it as fast as possible.
+
+## improve the Library
+add some `methods, classes, interfaces.....` anywhere, **please** Post a _description_ of each new method and variable, use simple english language to explain.
+
+## Create New Speedometer
+keep these in your mind when you want to create new Speedometer
+* extends `Speedometer` class.
+* implement abstract methods.
+* Override `onSizeChanged(int w, int h, int oldW, int oldH)` method.
+* Override `onDraw(Canvas canvas)` method.
+* add default Gauge values in `defaultValues()` method by call super for each, like so:
+```java
+   super.setBackgroundCircleColor(Color.TRANSPARENT);
+```
+* add default Speedometer values in `defaultSpeedometerValues()` method by call super for each, like so:
+```java
+   super.setSpeedometerColor(Color.RED);
+   super.setSpeedometerWidth(dpTOpx(40f));
+```
+* call `updateBackgroundBitmap();` at end of `onSizeChanged` method.
+* call `drawTicks(canvas);` inside `updateBackgroundBitmap()` method.
+* call `drawSpeedUnitText(canvas);` inside `onDraw` method.
+* call `drawIndicator(canvas);` inside `onDraw` method.
+* call `drawNotes(canvas);` at end of `onDraw` method.
+* add this lines at first of `updateBackgroundBitmap` method:
+```java
+   Canvas c = createBackgroundBitmapCanvas();
+   // draw on c canvas all drawing that doesn't change when speed update.
+```
+
+_so_, **your CustomSpeedometer class must be like this**:
+```java
+/**
+ * this Library build By Anas Altair, and this Speedometer added by YOUR_NAME.
+ * see it on <a href="https://github.com/anastr/SpeedView">GitHub</a>
+ */
+public class CustomSpeedometer extends Speedometer {
+
+    // add your Variables Here.
+
+    public CustomSpeedometer(Context context) {
+        this(context, null);
+    }
+
+    public CustomSpeedometer(Context context, AttributeSet attrs) {
+        this(context, attrs, 0);
+    }
+
+    public CustomSpeedometer(Context context, AttributeSet attrs, int defStyleAttr) {
+        super(context, attrs, defStyleAttr);
+    }
+
+    @Override
+    protected void defaultValues() {
+        // add default Gauge's values by call super.method like
+        // super.setBackgroundCircleColor(Color.TRANSPARENT);
+    }
+
+    @Override
+    protected void defaultSpeedometerValues() {
+        // add default Speedometer's values by call super.method like
+        // super.setStartEndDegree(135, 135 + 320);
+
+        // by default there is No Indicator, add indicator by:
+        // super.setIndicator(new TriangleIndicator(getContext())
+        //        .setIndicatorWidth(dpTOpx(25f))
+        //        .setIndicatorColor(0xff00e6e6));
+    }
+
+    @Override
+    protected void onSizeChanged(int w, int h, int oldW, int oldH) {
+        super.onSizeChanged(w, h, oldW, oldH);
+
+        // update your speedometer here if it depend on size.
+
+        // don't remove this line, and don't move up.
+        updateBackgroundBitmap();
+    }
+
+    @Override
+    protected void onDraw(Canvas canvas) {
+        super.onDraw(canvas);
+        // backgroundBitmap is Already painted.
+
+        // you can draw what do you want here.
+
+        // you must call this method to draw speed-unit Text.
+        // this method must call before drawIndicator(canvas) method.
+        drawSpeedUnitText(canvas);
+        // you must call this method to draw the indicator.
+        // put it wherever you want inside this method.
+        drawIndicator(canvas);
+
+        // you can draw what do you want here.
+
+        // don't remove this line, and don't move up.
+        drawNotes(canvas);
+    }
+
+    @Override
+    protected void updateBackgroundBitmap() {
+        // don't remove these lines.
+        Canvas c = createBackgroundBitmapCanvas();
+
+       // you must call drawTicks(c), but if you wont to draw
+       // min and max speed value use this.
+       if (getTickNumber() > 0)
+           drawTicks(c);
+       else
+           drawDefMinMaxSpeedPosition(c);
+    }
+
+    // add your custom methods here.
+}
+```
+these methods/varibles can help you in your custom Speedometer:
+
+method/varible | description
+--- | ---
+getSpeedText() | get correct speed as string to **Draw**.
+getUnit() | get unit string to **Draw**.
+getSize() | return width of SpeedometerRect.
+getSizePa() | return width of SpeedometerRect without padding.
+getWidthPa() | return View width without padding.
+getHeightPa() | return View height without padding.
+isSpeedometerTextRightToLeft() | if `true` you should draw unit string to the left of speed Text.
+getPadding() | use just this method to get padding.
+getDegree() | return correct degree of indicator.
+getStartDegree() | start degree where indicator and speedometer start.
+getEndDegree() | the end of speedometer, where indicator and speedometer must stop.
+getLowSpeedOffset() | return [0f, 1f], where `LowSpeedSection` must stop between **startDegree** and **endDegree** [what is this?](https://github.com/anastr/SpeedView/wiki/Usage#control-division-of-the-speedometer).
+getMediumSpeedOffset() | return [0f, 1f], where `MediumSpeedSection` must stop between **startDegree** and **endDegree** [what is this?](https://github.com/anastr/SpeedView/wiki/Usage#control-division-of-the-speedometer).
+drawDefMinMaxSpeedPosition (canvas) | use this method in `updateBackgroundBitmap()` method if you want to draw **Min** and **Max** speed text in default position.
+drawTicks (canvas) | use this method in `updateBackgroundBitmap()` method to draw [Ticks](https://github.com/anastr/SpeedView/wiki/Usage#ticks).
+unitTextPaint | you must use this paint to draw unit text.
+
+and also : `getSpeedometerWidth()`, `getMarkColor()`, `getIndicatorColor()`, `getCenterCircleColor()`, `getLowSpeedColor()`, `getMediumSpeedColor()`, `getHighSpeedColor()`, `getTextColor()`, `getBackgroundCircleColor()`, `getIndicatorWidth()`.
+
+## Build New Component
+_**components:**_ are small objects can be drawn on speedometer.
+
+just like [Indicators](https://github.com/anastr/SpeedView/wiki/Indicators) and [Notes](https://github.com/anastr/SpeedView/wiki/Notes), your component must have `draw()` method with `Canvas` parameter.