Rails Against The Machine

Just a mind dump. Why are you even reading this?

Thursday, 19 June 2008

Cleaner pixel level drawing with java

Need to change alpha transparency independently of colour so changing from index color to direct.
More bitmask fun

package services;

import java.awt.Point;
import java.awt.image.BufferedImage;
import java.awt.image.DataBufferInt;
import java.awt.image.DirectColorModel;
import java.awt.image.SampleModel;
import java.awt.image.WritableRaster;

public class ImageFactory
{

    private static int width = 255;
    private static int height = 255;

    public static BufferedImage Image()
    {
        // This creates an RGBA colormodel... I think.
        DirectColorModel colormodel = new DirectColorModel(32, 0xff000000, 0xff0000, 0xff00, 0xff);
        int[] pixels = generatePixels(width, height);
        SampleModel sample = colormodel.createCompatibleSampleModel(width, height);
        DataBufferInt data = new DataBufferInt(pixels, width * height);
        WritableRaster raster = WritableRaster.createWritableRaster(sample, data, new Point(0, 0));
        return new BufferedImage(colormodel, raster, false, null);
    }

    private static int[] generatePixels(int w, int h)
    {
        int[] pixData = new int[width * height];
        int i = 0;
        for (int y = 0; y < height; y++) {
            int red = (y * 255) / (height - 1);
            for (int x = 0; x < width; x++) {
                int green = (x * 255) / (width - 1);
                int blue = 128;
                int alpha = Math.max(0,x-y);
                pixData[i++] = (alpha << 32) | (red << 24) |
                        (green << 16) | (blue << 8);
            }
        }
        return pixData;
    }
}

posted by ~J # 10:03 0 Comments

Thursday, 5 June 2008

Cascading drop downs

Java script code using prototype

window.onload = init;

function init(){
        //
        if (field = $('parent_dropdown_id')) {       
            field.observe('change', function(e) {
                //make a request and get the json output
                new Ajax.Request('url_to_get_data_from', {
                    method:'get',
                    parameters: field.serialize(true),
                    onSuccess: function(transport){
                        var json = transport.responseText.evalJSON();
                        some_namespace.display(json);
                    }
                });      
            });
        }
    }
    
    var some_namespace= {
        display: function (data){
            var field = $('child_dropdown_id');
            opt= field.options;
            opt.length=0; //You delete by resizing the array
            for(var i=0;i<data.length;i++){
                opt[opt.length] = new Option(data[i][0],data[i][1]);
            }
        }
    }

On the server you just return a json opject to populate the drop down

posted by ~J # 06:37 0 Comments

Stable back url

Back buttons based on request.env["HTTP_REFERER"] tend to get broken by renders and redirects
Set it in the session with.

  def set_backurl 
    referer = request.env["HTTP_REFERER"]
    return false if !referer
    getIt = request.env["REQUEST_URI"].split("?")[1]
    if getIt.nil?
      getIt = ""
    else
      getIt = "?" + getIt if !getIt.match(/\?/)
    end
    session[:backurl]=referer + getIt
  end

get it with

    @backurl =session[:backurl]

posted by ~J # 06:30 0 Comments