Drawing Vectors
zooms
Posts: 4
I am using the propeller in a class project and I am trying to draw a vector based on a starting point, angle, and magnitude. I am going to use this to make a wheel spin using the tv and the graphics objects.
Comments
Good luck in your class project.
Baggers.
PS, don't forget to post pics of the finished project.
Perry
I used the vec function to create some clock type graphical elements see:
http://forums.parallax.com/showthread.php?p=682917
For a wheel you could make a vector sprite like a star for the spokes and use arc for the rim, then move the rim and move and rotate the spokes for the rotation effect as it rolls. Using PI in there somewhere will make it look more realistic.
Graham
PUB vec(x, y, vecscale, vecangle, vecdef_ptr) Draw a vector sprite x,y - center of vector sprite vecscale - scale of vector sprite ($100 = 1x) vecangle - rotation angle of vector sprite in bits[noparse][[/noparse]12..0] vecdef_ptr - address of vector sprite definition Vector sprite definition: word $8000|$4000+angle 'vector mode + 13-bit angle (mode: $4000=plot, $8000=line) word length 'vector length ... 'more vectors ... word 0 'end of definitionSo when defining a sprite you start at 0,0 if you do $8000 + 13bit angle then it will draw a line from 0,0 in that direction. If you did $4000 + 13bit angle then it will draw a point and the next vector will be drawn from there.
After the angle and type is defined the length of the vector.
The example from the demo of a triangle:
vecdef word $4000+$2000/3*0 ' draws a point at an angle zero degrees (notice * 0) from 0,0 word 50 ' a distance 50 away word $8000+$2000/3*1+1 ' draws a line at an angle of 360/3 degrees from that point word 50 ' of length 50 word $8000+$2000/3*2-1 ' draws a line at an angle of 2/3 360 degrees from that point word 50 ' length 50 word $8000+$2000/3*0 ' finishes with another horizontal line (angle 0) word 50 ' length 50 word 0 ' finish vector spriteAll angles are from the horizontal CCW. 0,0 in the sprite is the point that will be positioned at x,y as defined in the command vec.
If you draw your spokes comming out from 0,0 then any rotation will make them rotate around their centre.
Please do some experimentation and do actually read what is in graphics.spin to better understand it.
Graham
p.s. The pointer in my program is a vector sprite.
The angle is stored in 13 bits, this is %1111111111111 or $1FFF
zero represents both 0 degrees and 360 degrees so $1FFF represents just less than 360 and $2000 (which is $1FFF + 1) represents 360 degrees as well numerically but cannot be used because it is more than 13 bits however it can be divided up and used like in this case. The +1, and -1 used are to ensure that the total comes to 180 degrees, the total angle within a triangle accounting for the lack of fractional values I think.
Graham
I've been fooling around a bit, here's what I came up with for some spokes. I converted to 360 degrees to make it easier to read at a cost of resolution for angle.
-Martin
repeat gr.colorwidth(3,2) repeat k from 0 to 359 gr.clear gr.vec(0, 0, 100, $1fff * k / 360 , @vecdef) ' draw angle converted to 360 (much resolution loss) gr.copy(display_base) waitcnt(clkfreq/100 + cnt) . . . ' ALL angles are with respect to center, not last point ' All distances are from center as well vecdef word $4000 + ($1fff * 0 / 360) ' set a point at 0 degrees from center word 30 ' at distance of 30 word $8000 + ($1fff * 0 / 360) ' draw a line of 50 at 0 deg from center word 50 word $4000 + ($1fff * 30 / 360) ' set a point 30 degrees from center, distance 30 word 30 word $8000 + ($1fff * 30 / 360) ' draw a line 30 degrees off from cente, distance of 50, word 50 word $4000 + ($1fff * 60 / 360) word 30 word $8000 + ($1fff * 60 / 360) word 50 ' up to 330 degees......... word 0An alternate means to use one line draw at various angles from your loop:
repeat gr.colorwidth(3,2) repeat k from 0 to 359 gr.clear repeat i from 0 to 360 step 30 ' draw a vector every 30 degrees based on k + i gr.vec(0, 0, 100, $1fff * (k +i) / 360 , @vecdef) ' draw angle converted to 360 (much resolution loss) gr.copy(display_base) waitcnt(clkfreq/100 + cnt) ' ALL angles are with respect to center, not last point ' All distances are from center as well vecdef word $4000 + ($1fff * 0 / 360) ' set a point at 0 degrees from center word 30 ' at distance of 30 word $8000 + ($1fff * 0 / 360) ' draw a line of 50 at 0 deg from center word 50 word 0 ' end of defination▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
StampPlot - GUI and Plotting Software
Southern Illinois University Carbondale, Electronic Systems Technologies
Post Edited (Martin Hebel) : 10/26/2007 2:11:45 AM GMT
What I hinted to was a not very popular creative use of arc, such as:
centerX := 100 centerY := 100 length := 50 repeat repeat angle from 0 to 360 gr.copy(...) gr.clear ' line got lost during posting - will make it much more instructive! gr.arc(centerX , centerY , length, length, angle*$2000/360 , 0, 1, 3)Post Edited (deSilva) : 10/29/2007 5:17:48 PM GMT
Looks like I need to upgrade my graphics.spin it doesn't even have an arc command.
Graham
But - oops - did I delete the gr.clear as well? Sorry, the gr.clear should have stayed in it... darn on the fly editing of working code.
Graham
Indeed gr.arc(centerX , centerY , length, length, angle*$2000/360 , 0, 1, 3)
is not trivial...