CanvasUtils.java example

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umlet-master
package com.baselet.gwt.client.view;

import com.baselet.control.basics.geom.Rectangle;
import com.baselet.control.constants.SharedConstants;
import com.baselet.diagram.draw.helper.ColorOwn;
import com.baselet.diagram.draw.helper.ColorOwn.Transparency;
import com.baselet.element.GridElementUtils;
import com.baselet.element.interfaces.Diagram;
import com.baselet.gwt.client.base.Converter;
import com.google.gwt.canvas.client.Canvas;
import com.google.gwt.canvas.dom.client.Context2d;

public class CanvasUtils {

	private static final int EXPORT_BORDER = 10;

	public static String createPngCanvasDataUrl(Diagram diagram) {
		DrawCanvas pngCanvas = new DrawCanvas();
		// Calculate and set canvas width
		Rectangle geRect = GridElementUtils.getGridElementsRectangle(diagram.getGridElements());
		geRect.addBorder(EXPORT_BORDER);
		pngCanvas.clearAndSetSize(geRect.getWidth(), geRect.getHeight());
		// Fill Canvas white
		pngCanvas.getContext2d().setFillStyle(Converter.convert(ColorOwn.WHITE));
		pngCanvas.getContext2d().fillRect(0, 0, pngCanvas.getWidth(), pngCanvas.getHeight());
		// Draw Elements on Canvas and translate their position
		pngCanvas.getContext2d().translate(-geRect.getX(), -geRect.getY());
		pngCanvas.draw(false, diagram.getGridElementsByLayerLowestToHighest(), new SelectorNew(diagram)); // use a new selector which has nothing selected
		return pngCanvas.toDataUrl("image/png");
	}

	private static Canvas gridCanvas;

	public static void drawGridOn(Context2d context2d) {
		if (gridCanvas == null) {
			gridCanvas = Canvas.createIfSupported();
			gridCanvas.setCoordinateSpaceWidth(3000);
			gridCanvas.setCoordinateSpaceHeight(2000);
			int width = gridCanvas.getCoordinateSpaceWidth();
			int height = gridCanvas.getCoordinateSpaceHeight();
			Context2d backgroundContext = gridCanvas.getContext2d();
			backgroundContext.setStrokeStyle(Converter.convert(ColorOwn.BLACK.transparency(Transparency.SELECTION_BACKGROUND)));
			for (int i = 0; i < width; i += SharedConstants.DEFAULT_GRID_SIZE) {
				drawLine(backgroundContext, i, 0, i, height);
			}
			for (int i = 0; i < height; i += SharedConstants.DEFAULT_GRID_SIZE) {
				drawLine(backgroundContext, 0, i, width, i);
			}
		}
		context2d.drawImage(gridCanvas.getCanvasElement(), 0, 0);
	}

	private static void drawLine(Context2d context, int x, int y, int x2, int y2) {
		context.beginPath();
		context.moveTo(x + 0.5, y + 0.5); // +0.5 because a line of thickness 1.0 spans 50% left and 50% right (therefore it would not be on the 1 pixel - see https://developer.mozilla.org/en-US/docs/HTML/Canvas/Tutorial/Applying_styles_and_colors)
		context.lineTo(x2 + 0.5, y2 + 0.5);
		context.stroke();
	}
}