C & Gtk: drawing areas

Stween · 07-02-2003, 04:25 AM

Ello,

I've been fiddling about a little with GTK a little bit (nothing serious, I'm just looking to see how it all works), and something has puzzled me.

Drawing areas... the information in the official gtk tutorial is sparse on this topic (other than the scribble example, and brief searches aren't turning up much for me.

What I'd *really* like to know is, how do I set colours for individual pixels, be they drawn by the user clicking on the drawing area or from loading image data from disk? This has me kinda stumped.

But perhaps I'm just too tired...

Anyone here know much about gtk coding?

EscapeCharacter · 07-02-2003, 12:16 PM

so you are trying to have a drawing area to get random colors drawn where you click? if so you could do this by getting the x and y coordinates of the mouse and depending where that is on the drawing area set the color you want and XDrawPoint(or whatever the gtk equiv is).

note: XDrawPoint is a xlib routine. i dont know gtk but since it is based on xlib that should be a good starting point for you.

Stween · 07-03-2003, 12:48 PM

What I'm trying to do is load image data from disk - the image data is stored in C header files in an abnormal format. I can read in the data fine, what stumps me is how do I go from the data which I can read into handy arrays, to something that I can display.

I've been reading through the gdk stuff, and have started fiddling with gdk pixbuf's, which look like they might be the way to go, but I still can't set the individual pixels, and there seems to be no easy way to take my array of values and create a simple pixbuf out of them.

Ultimately, I'm trying to create a simple app that draws a few of these (they're small, 8x8 tiles), but setting pixel values seems to be the biggest hurdle here

The (small) application I'm writing here is as much a programming exercise to try and learn a little GTK and get used to more C, but I'd really like to get over this little issue - I can pretty much see how I'm doing everything other than this

Why isn't it as simple as 'pb[x][y].red= 0xFF'?!

EscapeCharacter · 07-03-2003, 04:35 PM

what format is the image? since you said it is included in a header file that makes me believe it may be a xpm which has its own xlib routines to handle it. libxpm and whatnot.

Stween · 07-04-2003, 04:27 AM

Quote:

Originally posted by EscapeCharacter
what format is the image? since you said it is included in a header file that makes me believe it may be a xpm which has its own xlib routines to handle it. libxpm and whatnot.

Ok, the map tiles themselves use a 256 colour palette which is selected from a 15-bit colour palette - this colour palette arranges colours as BGR (the reverse of what is normally used), with 5 bits per channel.

This is represented in the header file by an array of 256 16-bit unsigned numbers (presumably the most significant bit is ignored when looking at the 15-bits required for the colour).

What I'd be wanting to do would be read in both the tile data and the palette, and use the values in the tile data to lookup the appropriate palette colour and set the pixel to that.

In my mind, it's a really simple thing to achieve...

The only hazy bit is the difference between the 15-bit palette the tiles are using and the 24-bit palette I'd probably have to represent it with, but even then, a couple of bit shifting operations to get the RGB fields in the correct place would allow me to see what tiles are where; I can probably overlook wonky colours there

Stween · 07-06-2003, 06:52 AM

Although, thinking about it, I suppose I could read in the relevant data, output it to a file in xpm format, then load it that way...

Just seems like a horrible workaround ... but it might just work