// Copyright 2004 Adam Megacz, see the COPYING file for licensing [GPL]
package org.xwt;

/**
 *  <p>
 *  A block of pixels which can be drawn on.
 *  </p>
 *
 *  <p>
 *  Implementations of the Platform class should return objects
 *  supporting this interface from the _createPixelBuffer()
 *  method. These implementations may choose to use off-screen video
 *  ram for this purpose (for example, a Pixmap on X11).
 *  </p>
 *
 *  <p>
 *  Many of these functions come in pairs, one that uses ints and one
 *  that uses floats.  The int functions are intended for situations
 *  in which the CTM is the identity transform.
 *  </p>
 */
public abstract class PixelBuffer {

    /** draw the picture at (dx1, dy1), cropping to (cx1, cy1, cx2, cy2) */
    protected abstract void drawPicture(Picture source, int dx1, int dy1, int cx1, int cy1, int cx2, int cy2);

    /** fill a trapezoid whose top and bottom edges are horizontal */
    public abstract void fillTrapezoid(int x1, int x2, int y1, int x3, int x4, int y2, int color);

    /**
     *  Same as drawPicture, but only uses the alpha channel of the Picture, and is allowed to destructively modify the RGB
     *  channels of the Picture in the process.  This method may assume that the RGB channels of the image are all zero IFF it
     *  restores this invariant before returning.
     */
    public abstract void drawGlyph(Font.Glyph source, int dx1, int dy1, int cx1, int cy1, int cx2, int cy2, int rgb);

    // FEATURE: we want floats (inter-pixel spacing) for antialiasing, but this hoses the fastpath line drawing... argh!
    /** draws a line of width <tt>w</tt>; note that the coordinates here are <i>post-transform</i> */
    public void drawLine(int x1, int y1, int x2, int y2, int w, int color, boolean capped) {

	if (y1 > y2) { int t = x1; x1 = x2; x2 = t; t = y1; y1 = y2; y2 = t; }

	if (x1 == x2) {
            fillTrapezoid(x1 - w / 2, x2 + w / 2, y1 - (capped ? w / 2 : 0),
                          x1 - w / 2, x2 + w / 2, y2 + (capped ? w / 2 : 0), color);
            return;
        }

        // fastpath for single-pixel width lines
        if (w == 1) {
            float slope = (float)(y2 - y1) / (float)(x2 - x1);
            int last_x = x1;
            for(int y=y1; y<=y2; y++) {
                int new_x = (int)((float)(y - y1) / slope) + x1;
                if (slope >= 0) fillTrapezoid(last_x + 1, y != y2 ? new_x + 1 : new_x, y,
                                              last_x + 1, y != y2 ? new_x + 1 : new_x, y + 1, color);
                else fillTrapezoid(y != y2 ? new_x : new_x + 1, last_x, y,
                                   y != y2 ? new_x : new_x + 1, last_x, y + 1, color);
                last_x = new_x;
            }
            return;
        }

        // actually half-width
	float width = (float)w / 2;
	float phi = (float)Math.atan((y2 - y1) / (x2 - x1));
	if (phi < 0.0) phi += (float)Math.PI * 2;
	float theta = (float)Math.PI / 2 - phi;

	// dx and dy are the x and y distance between each endpoint and the corner of the stroke
	int dx = (int)(width * Math.cos(theta));
	int dy = (int)(width * Math.sin(theta));

	// slice is the longest possible length of a horizontal line across the stroke
	int slice = (int)(2 * width / Math.cos(theta));

	if (capped) {
	    x1 -= width * Math.cos(phi);
	    x2 += width * Math.cos(phi);
	    y1 -= width * Math.sin(phi);
	    y2 += width * Math.sin(phi);
	}

	fillTrapezoid(x1 + dx, x1 + dx, y1 - dy, x1 - dx, x1 - dx + slice, y1 + dy, color);           // top corner
	fillTrapezoid(x2 + dx - slice, x2 + dx, y2 - dy, x2 - dx, x2 - dx, y2 + dy, color);           // bottom corner
	fillTrapezoid(x1 - dx, x1 - dx + slice, y1 + dy, x2 + dx - slice, x2 + dx, y2 - dy, color);   // middle
    }

}