drawing Archives - "Where to now?"

Doodle Drawer – Brushes

January 7, 2013 / Jan Rabe / 0 Comments

At my Doodle Drawer app, I’ve played with a couple of “brushes”. The idea is to treat the connection lines differently.

shaded

sketched

fur

Basically the difference is that the line connections are drawn closer or further away from each line based on the formula of Harmony.

The ‘shaded brush’ looks like this:

@Override
    public void addConnections(Point nextPoint, int color, float strokeWidth) {
        ArrayList<Point> points = PointsList.points;
        for (int i = 0; i < points.size(); ++i) {
            Point curPoint = points.get(i);
            float b = curPoint.x - nextPoint.x;
            float a = curPoint.y - nextPoint.y;
            float distance = b * b + a * a;
            if (distance < 2000f * Config.DEVICE_DISPLAY_METRICS.density) {
                int alpha =  255-((int) (225f / 2000f * Config.DEVICE_DISPLAY_METRICS.density * distance));
                int newColor = Color.argb(alpha, Color.red(color), Color.green(color), Color.blue(color));
                LineList.connections.add(new Line(nextPoint, curPoint, newColor, strokeWidth * Config.BRUSH_PRESSURE * 0.5f));
            }
        }
    }

@Override

public void addConnections(Point nextPoint, int color, float strokeWidth) {

ArrayList<Point> points = PointsList.points;

for (int i = 0; i < points.size(); ++i) {

Point curPoint = points.get(i);

float b = curPoint.x - nextPoint.x;

float a = curPoint.y - nextPoint.y;

float distance = b * b + a * a;

if (distance < 2000f * Config.DEVICE_DISPLAY_METRICS.density) {

int alpha = 255-((int) (225f / 2000f * Config.DEVICE_DISPLAY_METRICS.density * distance));

int newColor = Color.argb(alpha, Color.red(color), Color.green(color), Color.blue(color));

LineList.connections.add(new Line(nextPoint, curPoint, newColor, strokeWidth * Config.BRUSH_PRESSURE * 0.5f));

}

The sketched brush looks like this:

    @Override
    public void addConnections(Point nextPoint, int color, float strokeWidth) {
        ArrayList points = PointsList.points;
        for (int i = 0; i &lt; points.size(); ++i) {
            Point curPoint = points.get(i);
            float b = curPoint.x - nextPoint.x;
            float a = curPoint.y - nextPoint.y;
            float distance = b * b + a * a;
            if (distance &lt; 10000 * Config.DEVICE_DISPLAY_METRICS.density &amp;&amp; Math.random() &gt; (distance / 10000 * Config.DEVICE_DISPLAY_METRICS.density)) {
                int alpha = 255 - ((int) ((225f / 2000f * Config.DEVICE_DISPLAY_METRICS.density) * distance));
                int newColor =  Color.argb(alpha, Color.red(color), Color.green(color), Color.blue(color));
                final float c = 0.2f;
                LineList.connections.add(new Line(new Point(nextPoint.x + (b * c), nextPoint.y + (a * c)), new Point(curPoint.x - (b * c), curPoint.y - (a * c)),newColor, strokeWidth * 0.5f * Config.BRUSH_PRESSURE));
            }
        }
    }

@Override

public void addConnections(Point nextPoint, int color, float strokeWidth) {

ArrayList points = PointsList.points;

for (int i = 0; i < points.size(); ++i) {

Point curPoint = points.get(i);

float b = curPoint.x - nextPoint.x;

float a = curPoint.y - nextPoint.y;

float distance = b * b + a * a;

if (distance < 10000 * Config.DEVICE_DISPLAY_METRICS.density && Math.random() > (distance / 10000 * Config.DEVICE_DISPLAY_METRICS.density)) {

int alpha = 255 - ((int) ((225f / 2000f * Config.DEVICE_DISPLAY_METRICS.density) * distance));

int newColor = Color.argb(alpha, Color.red(color), Color.green(color), Color.blue(color));

final float c = 0.2f;

LineList.connections.add(new Line(new Point(nextPoint.x + (b * c), nextPoint.y + (a * c)), new Point(curPoint.x - (b * c), curPoint.y - (a * c)),newColor, strokeWidth * 0.5f * Config.BRUSH_PRESSURE));

}

And the ‘fur brush’ looks like this:

    @Override
    public void addConnections(Point nextPoint, int color, float strokeWidth) {
        ArrayList points = PointsList.points;
        for (int i = 0; i &lt; points.size(); ++i) {
            Point curPoint = points.get(i);
            float b = curPoint.x - nextPoint.x;
            float a = curPoint.y - nextPoint.y;
            float distance = b * b + a * a;
            if (distance &lt; 4000f * Config.DEVICE_DISPLAY_METRICS.density &amp;&amp; Math.random() &gt; distance / 4000f * Config.DEVICE_DISPLAY_METRICS.density) {
                final float c = 0.5f;
                LineList.connections.add(new Line(new Point(nextPoint.x + (b * c), nextPoint.y + (a * c)), new Point(nextPoint.x - (b * c), nextPoint.y - (a * c)), color, strokeWidth * Config.BRUSH_PRESSURE * 0.5f));
            }
        }
    }

@Override

public void addConnections(Point nextPoint, int color, float strokeWidth) {

ArrayList points = PointsList.points;

for (int i = 0; i < points.size(); ++i) {

Point curPoint = points.get(i);

float b = curPoint.x - nextPoint.x;

float a = curPoint.y - nextPoint.y;

float distance = b * b + a * a;

if (distance < 4000f * Config.DEVICE_DISPLAY_METRICS.density && Math.random() > distance / 4000f * Config.DEVICE_DISPLAY_METRICS.density) {

final float c = 0.5f;

LineList.connections.add(new Line(new Point(nextPoint.x + (b * c), nextPoint.y + (a * c)), new Point(nextPoint.x - (b * c), nextPoint.y - (a * c)), color, strokeWidth * Config.BRUSH_PRESSURE * 0.5f));

}

Parametric Curves and deCasteljau Bezier Curves

December 29, 2012 / Jan Rabe / 2 Comments

Cubic Bezier Curves – Under the Hood from Peter Nowell on Vimeo.

You can drag the markers and open this example in new tab.

The core part of this practise clearly is the bezier curve. To get all points on the curve for 4 control points this would suffice.

/**
 * Computes deCasteljau p(t) for 4 control points.
 * 
 * @param t - portion on the graph, value between 0.0 and 1.0
 * @param cP - 4 control points [x,y]
 * @return point[x,y] - p(t)
 */
this.deCasteljau = function (t, cP) {
    return (1 - t) * (1 - t) * (1 - t) * cP[0][1]
        + 3 * (1 - t) * (1 - t) * t * cP[1][1]
        + 3 * (1 - t) * t * t * cP[2][1]
        + t * t * t * cP[3][1];
};

/**

* Computes deCasteljau p(t) for 4 control points.

* @param t - portion on the graph, value between 0.0 and 1.0

* @param cP - 4 control points [x,y]

* @return point[x,y] - p(t)

this.deCasteljau = function (t, cP) {

return (1 - t) * (1 - t) * (1 - t) * cP[0][1]

+ 3 * (1 - t) * (1 - t) * t * cP[1][1]

+ 3 * (1 - t) * t * t * cP[2][1]

+ t * t * t * cP[3][1];

};

However in order to use an arbitary amount of control points I use the following function. It’s recursively, so potentially it’ll explode the max available stack depth (no clue how much that is in js). But for now it’ll do the job.

/**
 * Computes deCasteljau p(t) for n-control points 
 *
 * @param cp - list of control points [][x,y]
 * @param r - amount points (init value : points.length-1)
 * @param i - start value (init value : 0)
 * @param t - portion on the graph (range between 0.0 and 1.0)
 *
 * @see http://stackoverflow.com/a/6271870 for n-control points
 *
 * @return point[x,y] - point on graph at p(t) 
 */
this.deCasteljau = function (cp, r, i, t) {
    if (r == 0) return cp[i];
    var p1 = this.deCasteljau(cp,r - 1, i, t);
    var p2 = this.deCasteljau(cp,r - 1, i + 1, t);
    return [(1 - t) * p1[0] + t * p2[0], (1 - t) * p1[1] + t * p2[1]];
};

/**

* Computes deCasteljau p(t) for n-control points

* @param cp - list of control points [][x,y]

* @param r - amount points (init value : points.length-1)

* @param i - start value (init value : 0)

* @param t - portion on the graph (range between 0.0 and 1.0)

* @see http://stackoverflow.com/a/6271870 for n-control points

* @return point[x,y] - point on graph at p(t)

this.deCasteljau = function (cp, r, i, t) {

if (r == 0) return cp[i];

var p1 = this.deCasteljau(cp,r - 1, i, t);

var p2 = this.deCasteljau(cp,r - 1, i + 1, t);

return [(1 - t) * p1[0] + t * p2[0], (1 - t) * p1[1] + t * p2[1]];

};

To use the function simply wrap a loop around with your favorite segments amount.

/**
 * Compute Points with deCasteljau.
 * 
 * @param minT - min t (init 0)
 * @param maxT - max t (init 1)
 * @param segments - amount segments, the more the smoother (init 20)
 * @param controlPoints - list of control points [n][x,y]
 * @return points[segments][x,y] points on bezier curve
 */
var computePoints = function(minT, maxT, segments, controlPoints) {
    var points = [segments];
    var t;
    // compute segments + 1 points
    for (var i = 0; i <= segments; ++i) {
        // compute t for t_min and t_max
        t = min_t + i / segments * (min_t + max_t);
        points[i] = this.deCasteljau(controlPoints,controlPoints.length - 1, 0, t);
    }
    return points;
};

/**

* Compute Points with deCasteljau.

* @param minT - min t (init 0)

* @param maxT - max t (init 1)

* @param segments - amount segments, the more the smoother (init 20)

* @param controlPoints - list of control points [n][x,y]

* @return points[segments][x,y] points on bezier curve

var computePoints = function(minT, maxT, segments, controlPoints) {

var points = [segments];

var t;

// compute segments + 1 points

for (var i = 0; i <= segments; ++i) {

// compute t for t_min and t_max

t = min_t + i / segments * (min_t + max_t);

points[i] = this.deCasteljau(controlPoints,controlPoints.length - 1, 0, t);

}

return points;

};

Now simply draw the points.

/**
 * Draw points.
 * 
 * @param context
 * @param points - list of points
 */
var draw = function (context, points) {

    context.beginPath();

    // check all segment lines
    for (var i = 1; i <= this.parameter.segments; ++i) {
        // draw curve [x,y]
        context.moveTo(points[i - 1][0], points[i - 1][1]);
        context.lineTo(points[i][0], points[i][1]);
    }
    context.closePath();

    // set drawing style
    context.lineWidth = 2; 
    context.strokeStyle = "#ff0000"; // line color

    // actually start drawing
    context.stroke();
}

/**

* Draw points.

* @param context

* @param points - list of points

var draw = function (context, points) {

context.beginPath();

// check all segment lines

for (var i = 1; i <= this.parameter.segments; ++i) {

// draw curve [x,y]

context.moveTo(points[i - 1][0], points[i - 1][1]);

context.lineTo(points[i][0], points[i][1]);

}

context.closePath();

// set drawing style

context.lineWidth = 2;

context.strokeStyle = "#ff0000"; // line color

// actually start drawing

context.stroke();

}

Et voilà! The animation idea is inspired by Johan Borgström‘s article about bezier curves.

This is my solution to cg2 exercersise a01.2-1.3.

Doodle Drawer

December 22, 2012 / Jan Rabe / 0 Comments

Inspired by Harmony from Mr. Doob (Ricardo Cabello) I made a little app called ‘Doodle Drawer’. The basic idea for some brushes is that it connects lines that has been drawn already and in case they’re close enough.

silly doodle

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Doodle Drawer – Brushes

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