zildo.fwk.gfx.filter.CircleFilter.java Source code

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Here is the source code for zildo.fwk.gfx.filter.CircleFilter.java

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/**
 * Legend of Zildo
 * Copyright (C) 2006-2011 Evariste Boussaton
 * Based on original Zelda : link to the past (C) Nintendo 1992
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

package zildo.fwk.gfx.filter;

import org.lwjgl.opengl.GL11;

import zildo.Zildo;
import zildo.client.ClientEngineZildo;
import zildo.monde.map.Point;

/**
 * Draws a circle around a specific center (Zildo !).<br/>
 * 
 * Mathematical explanation:<p/>
 * 
 * Each point respecting following equation must be shown :<br/>
 * (x - a) + (y - b) > r <p/>
 * 
 * So the screen is divided vertically into 3 areas :<ol>
 * <li>before circle : all is black</li>
 * <li>circle : each line has two roots from an equation derived from the first one
 * <li>after circle : all is black again</li>
 * </ol>
 * 
 * In order to calculate the derived equation, let's set a variable Y = (y - b) <br/>
 * So we have: <br/>
 * (x - a) + Y > r <br/>
 * wich gives : <br/>
 * x - 2ax + a + Y - r > 0 <p/>
 * 
 * If we calculate the delta : <br/>
 * D = (-2a) - 4 * (a + Y - r) <br/>
 * D = 4 * (a - r)<p>
 * 
 * So we deduce the 2 roots of the equation : <br/>
 * x1 = (2 * a - sqrt(D)) / 2 <br/>
 * x2 = (2 * a + sqrt(D)) / 2 <br/>
 * @author Tchegito
 *
 */
public class CircleFilter extends FadeScreenFilter {

    // Center of the circle
    public static Point center = new Point(Zildo.viewPortX / 2, Zildo.viewPortY / 2);

    // Coeff to get the circle drawn all over the screen
    private double coeffLevel = Math.sqrt(Math.pow(Zildo.viewPortX, 2) + Math.pow(Zildo.viewPortY, 2)) / 255f;

    @Override
    public boolean renderFilter() {

        // Get on top of screen and disable blending
        GL11.glMatrixMode(GL11.GL_MODELVIEW);
        GL11.glLoadIdentity();
        GL11.glMatrixMode(GL11.GL_PROJECTION);
        GL11.glPushMatrix();
        GL11.glTranslatef(0, -sizeY, 1);

        GL11.glColor3f(1f, 1f, 1f);

        GL11.glBindTexture(GL11.GL_TEXTURE_2D, textureID);

        GL11.glBegin(GL11.GL_QUADS);
        int radius = (int) (coeffLevel * (255 - getFadeLevel())); // + 20;
        int radiusSquare = (int) Math.pow(radius, 2);
        int col = 0;

        int sizeA = center.y - radius;
        int sizeB = Zildo.viewPortY - (center.y + radius);

        // 1) Draw the two areas outside the circle
        if (sizeA > 0) {
            ClientEngineZildo.ortho.boxOpti(0, 0, Zildo.viewPortX, sizeA, 2, null);
        }
        if (sizeB > 0) {
            ClientEngineZildo.ortho.boxOpti(0, center.y + radius, Zildo.viewPortX, sizeB, 2, null);
        }

        // 2) Draw the circle area
        int startI = Math.max(0, sizeA);
        int endI = Math.min(Zildo.viewPortY, center.y + radius);

        for (int i = startI; i < endI; i++) {
            int start = (int) Math.pow(i - center.y, 2);

            // Calculate DELTA and 2 roots x1 & x2
            double delta = 4 * (radiusSquare - start);
            double squareRootDelta = Math.sqrt(delta);
            int x1 = (int) (center.x - squareRootDelta / 2);
            int x2 = (int) (center.x + squareRootDelta / 2);
            ClientEngineZildo.ortho.boxOpti(0, i, x1, 1, col, null);
            ClientEngineZildo.ortho.boxOpti(x2, i, Zildo.viewPortX - x2, 1, col, null);
        }
        GL11.glEnd();
        GL11.glPopMatrix();

        GL11.glMatrixMode(GL11.GL_MODELVIEW);
        GL11.glDisable(GL11.GL_BLEND);

        return true;
    }

    public static void setCenter(int p_x, int p_y) {
        center.x = p_x;
        center.y = Zildo.viewPortY - p_y;
    }
}