RFR: JDK-8294680: Refactor scaled border rendering [v7]

[Alexey Ivanov]

On Fri, 13 Jan 2023 20:36:46 GMT, Harshitha Onkar <honkar at openjdk.org> wrote:

>> In this fix, the common code required for scaled border rendering is unified and added to SwingUtilities3. This is achieved by adding a functional interface to SwingUtilities3 and calling the the respective paintBorder function passed as functional parameter to the method.  
>> 
>> Following are the usual steps for any border scaling -
>> 
>> - Resetting transform.
>> - Calculating new width, height, x & y-translations.
>> - Perform the required border rendering.
>> - And at the end restore the previous transform.
>> 
>> To test the refactored code, 3 separate border scaling instances were taken (details below) and the SwingUtilities3.paintBorder, (containing the common functionality) was applied. All the tests associated with the respective border changes pass.
>> 
>> 1. EtchedBorder - [PR#7449](https://github.com/openjdk/jdk/pull/7449) - Test: ScaledEtchedBorderTest.java
>> 2. LineBorder - [PR#10681](https://github.com/openjdk/jdk/pull/10681) - Test: ScaledLineBorderTest & ScaledTextFieldBorderTest.java
>> 3. JInternalFrame Border - [PR#10274](https://github.com/openjdk/jdk/pull/10274) - Test: InternalFrameBorderTest.java
>> 
>> The advantage of this solution is - it avoids code repetition and can be reused across all the border classes requiring border scaling fix.
>
> Harshitha Onkar has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - copyright year updated
>  - formatting changes, docs added

src/java.desktop/share/classes/com/sun/java/swing/SwingUtilities3.java line 148:

> 146:     /**
> 147:      * Used within border classes to add specific border implementation details.
> 148:      */

Suggestion:

    /**
     * A task which paints an <i>unscaled</i> border after {@code Graphics}
     * transforms are removed. It's used with the
     * {@link #paintBorder(Component, Graphics, int, int, int, int, UnscaledBorderPainter)
     * SwingUtilities3.paintBorder} which manages changing the transforms and calculating the
     * coordinates and size of the border.
     */

src/java.desktop/share/classes/com/sun/java/swing/SwingUtilities3.java line 151:

> 149:     @FunctionalInterface
> 150:     public interface UnscaledBorderPainter {
> 151:         void paintUnscaledBorder(Component c, Graphics g,

Suggestion:

        /**
         * Paints the border for the specified component after the
         * {@code Graphics} transforms are removed.
         *
         * <p>
         * The <i>x</i> and <i>y</i> of the painted border are zero.
         * 
         * @param c the component for which this border is being painted
         * @param g the paint graphics
         * @param w the width of the painted border, in physical pixels
         * @param h the height of the painted border, in physical pixels
         * @param scaleFactor the scale that was in the {@code Graphics}
         *                    
         * @see #paintBorder(Component, Graphics, int, int, int, int, UnscaledBorderPainter) SwingUtilities3.paintBorder
         * @see javax.swing.border.Border#paintBorder(Component, Graphics, int, int, int, int) Border.paintBorder
         */
        void paintUnscaledBorder(Component c, Graphics g,

src/java.desktop/share/classes/com/sun/java/swing/SwingUtilities3.java line 159:

> 157:      * Performs common scaling transformation steps required for rendering
> 158:      * the border correctly at different scales.
> 159:      */

Suggestion:

    /**
     * Paints the border for a component ensuring its sides have consistent
     * thickness at different scales.
     * <p>
     * It performs the following steps:
     * <ol>
     *     <li>Reset the scale transform on the {@code Graphics},</li>
     *     <li>Call {@code painter} to paint the border,</li>
     *     <li>Restore the transform.</li>
     * </ol>
     *
     * @param c the component for which this border is being painted
     * @param g the paint graphics
     * @param x the x position of the painted border
     * @param y the y position of the painted border
     * @param w the width of the painted border
     * @param h the height of the painted border
     * @param painter the painter object which paints the border after
     *                the transform on the {@code Graphics} is reset
     */

src/java.desktop/share/classes/com/sun/java/swing/SwingUtilities3.java line 167:

> 165:         // Step 1: Reset Transform
> 166:         AffineTransform at = null;
> 167:         Stroke oldStk = null;

Suggestion:

        Stroke oldStroke = null;

Let's spell the word in full. It's used twice in the method and I see no reason to abbreviate it.

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PR: https://git.openjdk.org/jdk/pull/11571