Degrafa Sliding Progress Bar Component

This is the the first post in the series, and each one will highlight a different component we developed for various projects throughout the year.

ThoughtFaqtory has been working on numerous projects this year and one of them required our team to develop a host of custom components with a specific look and feel. We had a couple of choices but we are very familiar with Degrafa and decided to use it to skin our components.

In the example application above, the component gives the user feedback on the progress of the slide show. This can be very useful component to show feedback within a wizard style user interface.

The progress bar has quite a bit of logic to work out the size of the sub-sections and labels based on the available width and height. It also supports vertical layout but had no requirement for this in the project. The colours (background, active and inactive) can be set using styles. The animation is done using AnimateProperty with a slight delay, and the easing function can be set in the styles.

In our next post we will use Flex 4 to create the exact same component and wait for it… the source will be included. This version will contain user interaction and we may even go as far as adding multi-touch events.

More to come…

Flex, PNGs, and PDFs…

At ThoughtFaqtory we are continually encouraged to think outside of the box when challenges are presented.  A challenge was set recently by a pretty innocuous requirement from one of our clients.

This project required me to implement functionality that would allow the end user to export groups of images to PDF. The PDF needed to be high quality, 300 ppi (pixels per inch). After some searching I came across the AlivePDF website which appeared to be perfect for my requirements. Initially after using AlivePDF to generate a few PDFs, I couldn’t believe how easy it was to use and I thought that I had found Utopia. My joy however was short lived after the following error message was received:

AlivePDF had no alpha channel support for PNGs and the PNG encoder provided by Adobe always returns a PNG with an alpha channel. Even if you turned off the transparency you will get back a 32 bit ARGB PNG.

I continued searching for someone who had a method of successfully removing the alpha channel but my search proved fruitless. Hence I decided to do my own research into PNGs and found the following:

A valid PNG consists of:

PNG signature
IHDR chunk (only one)
IDAT chunk (one or more)
IEND chunk (only one)

The PNG signature:

89 50 4E 47 0D 0A 1A 0A.

The IHDR image header:

The IDAT chunks contain the image data.
The IEND chunk marks the end of the PNG.

The colour type under the IHDR chunk needs to be mentioned here as that is where the image type is defined.

After familiarizing myself with PNGs, I revisited Adobe’s PNGEncoder.as class again and eventually managed to make certain changes that allowed the removal of the alpha channel all together.

After all the research this ended up being a lot easier than I had originally thought, all that I needed to do was change the colour type and extract the RGB values. Adobe’s colour type was 6 (True colour with alpha) I changed it to 2 (True colour only). Next I needed to isolate and extract the RGB values, this was done with a bitwise right shift operation and a bitwise AND operation.

// Build IHDR chunk
 
var IHDR:ByteArray = new ByteArray();
IHDR.writeInt(w);
IHDR.writeInt(h);
IHDR.writeUnsignedInt(0x08020000); // True colour (no alpha)
IHDR.writeByte(0);
writeChunk(png, 0x49484452, IHDR);
 
// Isolate RGB values
 
for (var j:int = 0; j < w; j++)
{
	p = img.getPixel(j, i);
	IDAT.writeByte(p >> 16 & 0xFF);
	IDAT.writeByte(p >> 8 & 0xFF);
	IDAT.writeByte(p & 0xFF);
}

The changes implemented resulted in the removal of the Alpha channel which allowed me to successfully embedded the encoded PNG image into a PDF with AlivePDF. This was the first of many problems I had working with PDFs, maybe you will get to read about the others in the not too distant future. Attached below is a sample application that will embed a PNG into a PDF.