Triangle multicolored in OpenGl (Rosetta code)

[TempodiBasic]

Hi QB64coders
another task for Rosetta Code in QB64

Code: QB64: [Select]

1. 'Task
2. 'Display a smooth shaded triangle with OpenGL.
3. Screen _NewImage(600, 600, 32)
4. Dim Shared glInit As Integer
5. glInput = 0
6. Do While InKey$ = "": Loop
7. End
8.  
9.  
10. Sub _GL ()
11.     If glInit = 0 Then
12.         _glViewport 1, 1, 600, 600
13.         _glClearColor 0, 0, 0, 1
14.         glInit = -1
15.     End If
16.     _glClear _GL_COLOR_BUFFER_BIT
17.     _glBegin _GL_TRIANGLES
18.     _glColor4f 1, 0, 0, 1
19.     _glVertex2f -1, -1
20.     _glColor4f 0, 1, 0, 1
21.     _glVertex2f 0, 0
22.     _glColor4f 0, 0, 1, 1
23.     _glVertex2f 1, -1
24.     _glEnd
25. End Sub

[AndyA]

The Rosetta Code task name is 'OpenGL'.   ( https://rosettacode.org/wiki/OpenGL)

Had a hard time finding what it is we're supposed to be looking for. Did you already submit the code to Rosetta Code?  I didn't see a 'QB64' entry.

I dunno, maybe a SLEEP: SYSTEM at the end instead DO:WHILE loop, to keep CPU usage to a minimum.

By the way, nice, concise, clean code for the triangle.

[TempodiBasic]

Hi AndyA
thanks to evaluate my task.

Yes maybe better to post the link of the task! I'll do next time.

Did you already submit the code to Rosetta Code?  I didn't see a 'QB64' entry

I've posted before here to show the task to QB64 friends. I'll post soon if there is no better code to show.

[AndyA]

TempodiBasic,

Just a silly question, as I know nothing about OpenGL, is there a way to make the triangle cover the whole 600x600 screen?

[TempodiBasic]

@AndyA
the OpenGl graphic system has its own cohordinates and its primitive graphic functions....
the range of Y cohordinates is -1(bottom) +1 top --> the Y increases from bottom to top while in the standard graphic it goes from top to bottom
the range of x cohordinates is -1 (left) +1(right)
the center of the screen is 0,0
as you can see here.
https://raw.githubusercontent.com/AshishKingdom/OpenGL-Tutorials/gh-pages/images/first-triangle/coordinate_system.png
A first good tutorial is that of Ashish at this web address https://ashishkingdom.github.io/OpenGL-Tutorials/

A short answer is  change the 2nd vertex2f from 0,0 to 0,1   (vertex2f x,y)

[AndyA]

Yep, that's what I was trying to figure out. It's just like the X/Y axis I learned in school vs. the computer screen coordinates.

Thanks for the solution and the link to Ashish's OpenGL tutorial page.

[bplus]

It would be nice to work with any 3 given points (that fit on screen) and any 3 colors for a Rosetta post.

[TempodiBasic]

@bplus
IMHO you can have two way to got this....

the first is simpler
make at random the 3 vertex cohordinates in the range of -1 to +1 for the X and Y
 make at random the RGBA components of color in the range of 0 to +1 (0-255)
and you got it
as here

Code: QB64: [Select]

1. 'Task
2. 'Display a smooth shaded triangle with OpenGL changing vertex's values
3. ' and color's values.
4. Screen _NewImage(600, 600, 32)
5. Dim Shared glInit As Integer, GlNew As Integer
6. glInput = 0
7. Do While InKey$ = ""
8.     If GlNew > 100 Then GlNew = 0 Else GlNew = GlNew + 1
9. Loop
10. End
11.  
12.  
13. Sub _GL ()
14.     Static r1, r2, r3, g1, g2, g3, b1, b2, b3, x1, x2, x3, y1, y2, y3
15.     If glInit = 0 Then
16.         _glViewport 1, 1, 600, 600
17.         _glClearColor 0, 0, 0, 1
18.         glInit = -1
19.     End If
20.     _glClear _GL_COLOR_BUFFER_BIT
21.  
22.     If GlNew = 1 Then
23.         r1 = Rnd * 1.0
24.         r2 = Rnd * 1.0
25.         r3 = Rnd * 1.0
26.         g1 = Rnd * 1.0
27.         g2 = Rnd * 1.0
28.         g3 = Rnd * 1.0
29.         b1 = Rnd * 1.0
30.         b2 = Rnd * 1.0
31.         b3 = Rnd * 1.0
32.  
33.         x1 = (Rnd * 2.0) - 1
34.         y1 = (Rnd * 2.0) - 1
35.         x2 = (Rnd * 2.0) - 1
36.         y2 = (Rnd * 2.0) - 1
37.         x3 = (Rnd * 2.0) - 1
38.         y3 = (Rnd * 2.0) - 1
39.     End If
40.  
41.     _glBegin _GL_TRIANGLES
42.     _glColor4f r1, g1, b1, 1
43.     _glVertex2f x1, y1
44.     _glColor4f r2, g2, b2, 1
45.     _glVertex2f x2, y2
46.     _glColor4f r3, g3, b3, 1
47.     _glVertex2f x3, y3
48.     _glEnd
49. End Sub

the second way is to port the GL part of code from this demo in which I use a very fine your program to show the other two graphic output : normal or starndard graphic an the OpenGl graphic while in your original work you have greatly mastered the Maptriangles mode. https://www.qb64.org/forum/index.php?topic=3334.msg126287#msg126287

[bplus]

@TempodiBasic Good changes! Could the switching to a new triangle be smoothed out maybe with _delay or _limit?

[TempodiBasic]

@bplus
you're right! Using _delay can do a smoother changing of the aspect of the triangle!
here a way to get this:

Code: QB64: [Select]

1. 'Task
2. 'Display a smooth shaded triangle with OpenGL changing vertex's values
3. ' and color's values.
4. Screen _NewImage(600, 600, 32)
5. Dim Shared glInit As Integer, GlNew As Integer
6. glInput = 0
7. Do While InKey$ = ""
8.     If GlNew = 100 Then GlNew = 0 Else GlNew = GlNew + 1
9.     _Delay .002
10. Loop
11. End
12.  
13.  
14. Sub _GL ()
15.     Static r1, r2, r3, g1, g2, g3, b1, b2, b3, x1, x2, x3, y1, y2, y3
16.     If glInit = 0 Then
17.         _glViewport 1, 1, 600, 600
18.         _glClearColor 0, 0, 0, 1
19.         glInit = -1
20.     End If
21.     _glClear _GL_COLOR_BUFFER_BIT
22.  
23.     If GlNew = 1 Then
24.         r1 = Rnd * 1.0
25.         r2 = Rnd * 1.0
26.         r3 = Rnd * 1.0
27.         g1 = Rnd * 1.0
28.         g2 = Rnd * 1.0
29.         g3 = Rnd * 1.0
30.         b1 = Rnd * 1.0
31.         b2 = Rnd * 1.0
32.         b3 = Rnd * 1.0
33.  
34.         x1 = (Rnd * 2.0) - 1
35.         y1 = (Rnd * 2.0) - 1
36.         x2 = (Rnd * 2.0) - 1
37.         y2 = (Rnd * 2.0) - 1
38.         x3 = (Rnd * 2.0) - 1
39.         y3 = (Rnd * 2.0) - 1
40.     End If
41.  
42.     _glBegin _GL_TRIANGLES
43.     _glColor4f r1, g1, b1, 1
44.     _glVertex2f x1, y1
45.     _glColor4f r2, g2, b2, 1
46.     _glVertex2f x2, y2
47.     _glColor4f r3, g3, b3, 1
48.     _glVertex2f x3, y3
49.     _glEnd
50. End Sub

[bplus]

Hmm... that GL stuff seems to be working under it's own clock???

[TempodiBasic]

@bplus
in QB64 Opengl is a parallel process to the ordinary code. However the GPU is another chip parallel to the CPU.