GFAgraphics - Revision history

>Wongck at 12:28, 13 October 2011

2011-10-13T12:28:34Z

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	~~[[Category:~~Tutorials]]

>Wongck at 12:25, 13 October 2011

2011-10-13T12:25:22Z

← Older revision		Revision as of 08:25, 13 October 2011
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	[[Category:Tutorials]]		[[Category:Tutorials]]

>Silver Surfer: Added category

2009-05-02T20:23:17Z

Added category

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>Silver Surfer: Added category

2009-05-02T17:16:18Z

Added category

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>Simonsunnyboy at 17:22, 13 April 2007

2007-04-13T17:22:02Z

← Older revision		Revision as of 13:22, 13 April 2007
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	That should draw a continuous line through a set of 20 random points.		That should draw a continuous line through a set of 20 random points.

			There is another command to draw continuous sets of lines, the POLYLINE command. Refer to your GFABASIC manual on that one.

			'''Boxes and other rectangles'''

			You will probably want to draw some boxes as well. With the following knowledge you could something like this:

			CLS
			COLOR 1
			LINE 10,10,100,10
			LINE 100,10,100,100
			LINE 100,100,10,100
			LINE 10,100,10,10

			That should draw a box on screen but you have to use 4 commands, one for each side of the box. GFABASIC can do this in one go for you. Just use the BOX command. It takes two coordinates as parameters, the upper left corner and the lower right corner of your box. In the case above the following would do the same, and much faster:

			BOX 10,10,100,100

			Let's use the accumulated knowledge to draw a pattern on screen:

			CLS
			FOR x%=0 to 19
			FOR y%=0 to 10
			COLOR 1
			BOX x%16,y%16,x%16+14,y%16+14
			COLOR 3
			LINE x%16,y%16+14,x%16+14,y%16
			NEXT y%
			NEXT x%

			The screen should fill with a pattern of boxes that have a diagonal line inside. Color monitor users will see different colors too :)

			Another variation of drawing rectangles is to give them rounded edges. Simply write RBOX instead of BOX and the corners of your box are now rounded. Try the following:

			CLS
			FOR r%=10 TO 140 STEP 10
			RBOX 160-r%,100-r%,160+r%,100+r%
			NEXT r%

			It is quite easy to use.

			'''Round 'nd round'''

			GFABASIC can also draw circles and ellipses for you. To draw circles you use the, surprise surprise, CIRCLE command. It takes 3 parameters, a pair of coordinates and the radius of the circle you want to draw. The coordinate pair describes the center point of the circle you are going to draw onto the screen. The radius is simply measured in pixels as well. Let's try it out:

			CLS
			COLOR 1
			FOR r%=10 TO 90 STEP 10
			CIRCLE 150,100,r%
			NEXT r%

			If you look quickly, you should see that the diameter of the circle is growing with every iteration of the loop.
			One can also draw arcs with the CIRCLE command but I leave that up to you GFA manual to find out how.

			Let's go on and draw some ellipses. They use the ELLIPSE command and simply take another radius parameter. The first radius describes the horizontal size of the ellipse and the second one the vertical size. So it is quite easy. Try the following slightly different program:

			CLS
			COLOR 1
			FOR c%=20 TO 90 STEP 10
			ELLIPSE c%,100,c%,c%/2
			NEXT c%

			It will just draw a pattern consisting of growing ellipses on screen.

			'''Filled structures'''

			Sofar you have only drawn lines and single pixels. How about filling the void with some color and/or pattern? You can select a color and pattern to use for filled objects with the DEFFILL command. Its syntax is as follows:

			DEFFILL color.nr%,pattern.set%,pattern%

			The parameters are easy to explain. The color number specifies the number of color you want to use for the fill. The pattern set allows you to select between 3 different sets of fill styles but let me tell you right here, the first one is pretty boring. The pattern index itself goes up to 32. Let me show you with a simple program:

			CLS
			FOR s%=1 to 3
			FOR c%=0 to 31
			DEFFILL 1,s%,c%
			PBOX c%8,s%30,c%8+7,s%30+29
			NEXT c%
			NEXT s%

			Noted the PBOX command? It does the same as BOX but fills the box right away. That works with the other comamnds as well so you have PCIRCLE, PELLIPSE and PRBOX at your hand as well. But you can also fill a single location on screen. This floodfill will even follow any irregularities in your graphics on screen. Use the FILL command as follows:

			FILL x%,y%

			x% and y% simply form another coordinate pair just like the PLOT command did. Try it out with the following program:

			CLS
			COLOR 1
			FOR x%=0 to 319 STEP 5
			FILL 0,0,x%,195
			NEXT x%
			DEFFILL 3,2,4
			FILL 0,199

			The FILL command is pretty slow as you can see so I recommend to use it only to prepare graphics and store them to disk and/or memory for later use.

			That should be sufficient for now. In the next tutorial I'll tell you how to change the colors used in your screen and how to manipulate blocks of graphics.

			For the moment enjoy yourself and experiment with the graphical power of GFABASIC!

	back to [[GFA Tutorial]]		back to [[GFA Tutorial]]

>Simonsunnyboy at 16:40, 13 April 2007

2007-04-13T16:40:13Z

@@ Line 8: / Line 8: @@
 The amount of dots you can manipulate is dictated by the current screen resolution. The ST offers 3 different resolutions. By default GFABASIC starts your program in the current one so if you did boot GFA from a medium resolution desktop your program will use medium resolution too. (One can change that behaviour but that is not the goal of this part of the tutorial.)
-The screen resoultions differ on their size and the amount of colors you can use to draw the picture. Without tricks the ST offers the following video modes:
+The screen resolutions differ on their size and the amount of colors you can use to draw the picture. Without tricks the ST offers the following video modes:
 * ST-LOW: 320x200 pixels, 16 colors
 * ST-MED: 640x200 pixels, 4 colors
 * ST-HIGH: 640x400 pixels, 2 colors
 back to [[GFA Tutorial]]

>Simonsunnyboy at 16:20, 13 April 2007

2007-04-13T16:20:36Z

New page

'''Introduction to graphics'''

Thanks to the VDI GFABASIC offers the coder a wealth of commands to draw something on screen.
This part of the tutorial aims to help you getting started with graphics from GFABASIC.

First of all you have to understand how a nice picture works on the Atari ST. Everything you see on your screen is made up from tiny little dots. With the various graphics commands you can manipulate all of those dots to display anything on screen.

The amount of dots you can manipulate is dictated by the current screen resolution. The ST offers 3 different resolutions. By default GFABASIC starts your program in the current one so if you did boot GFA from a medium resolution desktop your program will use medium resolution too. (One can change that behaviour but that is not the goal of this part of the tutorial.)

The screen resoultions differ on their size and the amount of colors you can use to draw the picture. Without tricks the ST offers the following video modes:

* ST-LOW: 320x200 pixels, 16 colors
* ST-MED: 640x200 pixels, 4 colors
* ST-HIGH: 640x400 pixels, 2 colors

back to [[GFA Tutorial]]