How does Matrix.postScale( sx, sy, px, py) work?
Overview
The `Matrix.postScale(sx, sy, px, py)` method in Android’s Canvas API is used to apply a scaling transformation to a Canvas. This method scales the canvas around a specific pivot point.
Parameters
The `postScale()` method takes four parameters:
* **sx:** The scaling factor along the x-axis.
* **sy:** The scaling factor along the y-axis.
* **px:** The x-coordinate of the pivot point.
* **py:** The y-coordinate of the pivot point.
Explanation
* **Scaling:** The `sx` and `sy` parameters determine the scaling factor for the x and y axes respectively. A value greater than 1 will enlarge the canvas, while a value less than 1 will shrink it.
* **Pivot Point:** The `px` and `py` parameters define the point around which the scaling will occur. This means that the pivot point will remain fixed, while everything else scales relative to it.
Example
“`java
// Create a new Canvas
Canvas canvas = new Canvas();
// Create a Matrix object
Matrix matrix = new Matrix();
// Scale the canvas by a factor of 2 around the center point (100, 100)
matrix.postScale(2, 2, 100, 100);
// Apply the transformation to the canvas
canvas.setMatrix(matrix);
“`
Visual Representation
Imagine a rectangle with its center at (100, 100). Applying `Matrix.postScale(2, 2, 100, 100)` will double the size of the rectangle while keeping its center point fixed.
Comparison
| Method | Description |
| ————————————- | —————————————————————————————- |
| `Matrix.preScale(sx, sy, px, py)` | Applies scaling before other transformations in the matrix. |
| `Matrix.postScale(sx, sy, px, py)` | Applies scaling after other transformations in the matrix. |
Common Use Cases
* **Zooming:** Scaling the canvas by a factor greater than 1 to magnify an area.
* **Resizing:** Scaling the canvas to fit a specific size or aspect ratio.
* **Custom Transformations:** Combining scaling with other transformations like translation or rotation to create complex visual effects.