How to draw those smooth circles in Photoshop?

Hi!

Im working on a paint program with layers like in photoshop, and im having some problems drawing the really smooth circles that photoshop do.

i've made a function for anti-aliasing if that's nessesary...

when selecting a quite big size on the airbrush in photoshop you get a nice gradient circle...when i made a function like this, it doesnt fill all the pixels it should and it fills some of them twice.

can you please help me with the code....



here's some of the code i use:

VB Code:

For Radius = 0 to TempRadius
    For Angle = 0 to Pi2 Step 1 / Radius
        X = Cos(Angle) * Radius
        Y = Sin(Angle) * Radius
    Next
Next

this will not draw gradient thou...but it draws a filled circle...
please help me fix this code.

look at this image...
the filled circle at the left is how i want it to look....(i can fix the gradient myself later on...)
the circle at the right is how it looks...

http://www.vbforums.com/attachment.p...postid=1501351

it's drawn with rgb(255,0,0) and 50% opacity....you can see that some pixels are drawn on top of each other...

Circle drawing works different. First you calculate the bounding square (or rectangle, for ellipses). The you go through it top down. For each line you calculate how many pixels to the left and right from the center you have to go and color them. You'll want to color each pixel seperatly to be ready for patterns and gradients.

It works like this:
Radius: 3
Center: (3,3)
Bounding Square: (0,0)->(6,6)

Code:

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######
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When you get to patterns or gradients, you simply have to calculate the color for each pixel just before setting it.
E.g. linear gradient from white to black, starting at 0,0 and ending at 6,6. Distance: sqrt(6*6+6*6)
Pixel at 2,2. Distance to gradient start: sqrt(2*2+2*2). Distance to gradient end: sqrt(4*4+4*4). This means it is one third to black. Pixel result is one third end color (RGB 0,0,0) and two thirds start color (RGB 255,255,255), resulting in ~ RGB 170,170,170. Set pixel 2,2 to this color. Advance to next pixel to be colored and repeat.

If I may add: those computations are the reason why all serious drawing apps are written in C++: computations simply catch VB at its worst.

Quote:

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Originally posted by CornedBee
If I may add: those computations are the reason why all serious drawing apps are written in C++: computations simply catch VB at its worst.

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Yes i know...that's why im making a dll in c++ :)

i changed to something like this:

VB Code:

for angle = 0 to 2*Pi step 1/radius
    y=cos(angle)*radius
    for x=sin(2*pi-angle) *radius to sin(angle)*radius
        setpixel
    next
next

it works pretty allright.

now there's another program with the layers.
they work, but they're really slow cus when adding a pixel to a layer i redim an 1d array and add the x, y, opacity, r, g, b values...
the problem here is when painting above another pixel that pixel gets drawn 2 times or even more times if you draw alot...

i want to make a loop that checks if 2 pixels are at the same x and y position and then mix them together (in the array) and then remove one of them.

how should this be done?
something like this:

VB Code:

for layer = 0 to layercount -1
    for i = 0 to layers(layer).pixelcount-1
        for j = 0 to layers(layer).pixelcount-1
            if i<>j then
                if layers(layer).pixels(i).x = layers(layer).pixels(j).x _
                and layers(layer).pixels(i).y = layers(layer).pixels(j).y _
                then
                    'fix pixels
                end if
            end if
        next
    next
next

how should the code for "fixing" the pixels be?
should i take the average of the 2 pixel colors?
how about the opacity? average too?

here's my program:


do you think that its better to make a 2d array for the pixels?
so i dont have to store the x and y...cus then i can "mix" the pixels when drawing them instead of making a huge loop-in-loop-in-loop to check all pixels...

sorry...forgot to attach

The anti-aliasing results in non-opaque results.

Even at full opacity.

It's also very slow....

yes i know that it's really slow...im working on the speedups...

the reason why the aa is non-opaque is because i didnt get the pixels drawn correctly so there are some gaps between the lines.

What happens if you use a smaller interval to fill the circle? I know its slower, but if this works, then it can be optimized upon...

Better yet, can you draw filled triangles?

Still I think scanline-by-scanline is a far better technique to draw circles. Much faster, much less wasted time.

i think i'll try that method...

Hi Cyborg,

Hae Drawing circles will consume time... cuz that function has to compute.. I guess cornedbee has a point...

we can figure out the pixcel locations easily and set the pixcel color..

I will give a try and give you some code..

I tried with drawing circles on picbox.. it was fine ...

Regards,
Pradeep

Hi Cyborg,

All I had to do was change the DrawWidth.. This is easy..

Paste this code.in a form and place a PictureBox as pic.

VB Code:

Dim lRed        As Long
Dim lGreen      As Long
Dim lBlue       As Long
 
Dim fRedStp     As Single
Dim fGreenStp   As Single
Dim fBlueStp    As Single
    
Private Sub Form_Load()
    SetParams vbWhite, vbRed
    pic.DrawWidth = 2
    pic.AutoRedraw = True
End Sub
 
Private Sub pic_Click()
pic.Cls
Dim i As Integer
 
For i = 0 To 100
pic.ForeColor = BlendColors(i)
pic.Refresh
pic.Circle (pic.ScaleWidth \ 2, pic.ScaleHeight \ 2), i
Next
End Sub
Private Sub SetParams(StartColor As ColorConstants, EndColor As ColorConstants)
    
    Dim divVal As Single
    
    divVal = Sqr((pic.ScaleHeight ^ 2) + (pic.ScaleWidth ^ 2)) / 2
    
    lRed = (StartColor And &HFF& )
    lGreen = (StartColor And &HFF00& )  / &H100&
    lBlue = (StartColor And &HFF0000)  / &H10000
 
    fRedStp = CSng((EndColor And &HFF& ) - lRed) / divVal
    fGreenStp = CSng(((EndColor And &HFF00&) / &H100& ) - lGreen) / divVal
    fBlueStp = CSng(((EndColor And &HFF0000 )  /  &H10000 ) - lBlue) / divVal
  
End Sub
 
Private Function BlendColors(i As Integer) As Long
 
    BlendColors = RGB(Abs((lRed + i * fRedStp)), Abs((lGreen + i * fGreenStp)), _
    Abs((lBlue + i * fBlueStp)))
 
End Function

i didnt look through your code but i think it would be easy if i just made a function that looks through the lines as a square and check if the distance from a point is closer than the radius.

Hae..... The code is to draw a grad circle..

But Look at this..

Set the Picture Box DrawWidth to '2'.

See the attached picture...

Regards,
Pradeep

http://www.vbforums.com/attachment.p...postid=1506592

I'd try the scanline method.

Here's a function I wrote to accomplish this.

VB Code:

Sub DrawCircle(ByVal x As Long, ByVal y As Long, ByVal radius As Long)
Dim dY As Long, dx As Long
For dY = -radius To radius 'scan lines vertically
For dx = -1 * Sqr(Abs(radius ^ 2 - dY ^ 2)) To Sqr(Abs(radius ^ 2 - dY ^ 2)) 'calculate left x and right x for given y
PSet (x + dx, y + dY), vbRed 'draw at offset
Next
Next
End Sub

I have modified my function to do gradients:

VB Code:

Sub DrawCircle(ByVal X As Long, ByVal Y As Long, ByVal radius As Long)
Dim dY As Long, dx As Long, dist As Single
For dY = -radius To radius
For dx = -1 * Sqr(Abs(radius ^ 2 - dY ^ 2)) To Sqr(Abs(radius ^ 2 - dY ^ 2))
dist = Sqr(dx ^ 2 + dY ^ 2) 'compute distance
PSet (X + dx, Y + dY), RGB(dist / radius * 255, 0, 0) 'color point based on dist and radius
Next
Next
End Sub

I've developed yet another method to smoothly gradient onto a background.

VB Code:

'declares
Private Declare Function GetPixel Lib "gdi32" (ByVal hdc As Long, ByVal x As Long, ByVal y As Long) As Long
Private Declare Function SetPixelV Lib "gdi32" (ByVal hdc As Long, ByVal x As Long, ByVal y As Long, ByVal crColor As Long) As Long
 
'----
 
Sub DrawCircle(ByVal x As Long, ByVal y As Long, ByVal radius As Long, ByVal cR As Long, ByVal cG As Long, ByVal cB As Long)
Dim dY As Long, dx As Long, dist As Long, iColor As Long, r As Long, g As Long, b As Long
For dY = -radius To radius Step 1
For dx = -1 * Sqr(Abs(radius ^ 2 - dY ^ 2)) To Sqr(Abs(radius ^ 2 - dY ^ 2)) Step 1
iColor = GetPixel(hdc, x + dx, y + dY)
    r = (iColor And &HFF&)
    g = (iColor And &HFF00&) \ &H100&
    b = (iColor And &HFF0000) \ &H10000
 
dist = Sqr((dx) ^ 2 + (dY) ^ 2)
dr = dist / radius
idr = 1 - dr
 
r = (r * dr) + (cR * idr)
g = (g * dr) + (cG * idr)
b = (b * dr) + (cB * idr)
 
SetPixelV hdc, x + dx, y + dY, RGB(r, g, b)
Next
Next
End Sub

CANT WE DRAW CIRCLES FROM RADIUS = 0 to MAX BY SETTING DrawWidth = 2 for the PICTURE BOX

WHICH WOULD SOLVE.... :mad:


:D

Quote:

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Originally posted by pradeepkrao
CANT WE DRAW CIRCLES FROM RADIUS = 0 to MAX BY SETTING DrawWidth = 2 for the PICTURE BOX

WHICH WOULD SOLVE.... :mad:


:D

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My scanline sub offers blending onto the background, and can draw a circle of radius 50 in about 80 ms.

Which is probably what he wanted in the first place.

here's a new version of my paint program...

i've managed to make the drawing look good...did it like this

VB Code:

For tempx = -radius To radius
    For tempy = -radius To radius
        If getdistance(tempx,tempy,0,0) <= radius Then
            'now the pixel is in the circle and can be drawn.
            'for the gradient i used a sin curve from 0 to 1
            'and multiplied it by the brightness.
         End If
    Next
Next

no other changes are made, so its still really slow....

could you please help me find a way to make a 2d array that can be redimmed properly?

Hae Sorry .. I dint read the post fully....

Cyborg sent me a pm anyway..

I'd suggest working with the entire 32bit DIB, then use AlphaBlend to blt each layer with the extra byte for the alpha mask.

i'll just make a 1d field instead

Quote:

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Originally posted by cyborg
i'll just make a 1d field instead

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AlphaBlend API is hardware accelerated. So it'll take some load off the cpu, freeing resources for your other computations.

You may also want to look into GDI+.

Perhaps DDraw.

Atleast utilize some MMX or SSE extensions. You can do this fairly easily in C using ASM.

I hear the intel site has the instruction documentation.

Otherwise, google it.

well...does the alphablend api blend each pixel with different alpha value?...thats the whole point with this program ;)

Of course.

The API reference:

http://msdn.microsoft.com/library/de...tmaps_6ig4.asp

Explains the blend type:

http://msdn.microsoft.com/library/de...tmaps_3b3m.asp

does it work with win98 and earlier versions?

I think it works with 98, but nothing earlier.

Quote:

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Originally posted by cyborg
does it work with win98 and earlier versions?

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It works with 98... even though it's over 5 years old!