Static text on OpenGLContext

[ehj666]

I am porting a bunch of raw opengl code and trying to integrate it with OpenGLContext. With direct OpenGL calls in Delphi (Windows) and directly managing device contexts, I was able to just drop TLables for example on the same canvas. When I do that with OpenGLContext they hardly display at design time and not at all at run time.

What is the prescribed method for putting static text into the OpenGLContext? This text would for instance display X, Y mouse positions as the objects rendered through opengl are manipulated, thus should not be affected by pan, zoom, rotate, etc.

Thanks

[Handoko]

I'm not an expert in OpenGL, I may be wrong.

OpenGL (OpenGLContext) doesn't has feature to display text. You have to use extra library to do it or you can do as what I do. I display text on OpenGL by displaying bitmap (font texture), which I have prepared before.

This my code, which works but actually I don't remember how it works 

Code: Pascal  [Select][+][-]

1.   // GL preparation
2.   glLoadIdentity;
3.   glTranslatef(FXreal + Xtext, FYreal, 0);
4.   glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
5.   glEnable(GL_TEXTURE_2D);
6.   glEnable(GL_BLEND);
7.   glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
8.   glTexImage2D(GL_TEXTURE_2D, 0, 4, FTextureWidth, FTextureHeight, 0, GL_RGBA,
9.     GL_UNSIGNED_BYTE, Pointer(FTextureBuffer));
10.  
11.   // Draw the text
12.   glBegin(GL_QUADS);
13.   glColor3ub(255, 255, 255);
14.   glTexCoord2f(0, 0);
15.   glVertex3f(0, 0, 0);
16.   glTexCoord2f(1, 0);
17.   glVertex3f(Wtext, 0, 0);
18.   glTexCoord2f(1, 1);
19.   glVertex3f(Wtext, FHreal, 0);
20.   glTexCoord2f(0, 1);
21.   glVertex3f(0, FHreal, 0);
22.   glEnd();

[ehj666]

If I understand what you are saying, I do not think that is going to work. The text needs to update as the mouse moves for example, just like in the Lazarus environment where it tracks X and Y positions in the designer.

I could put another panel next to the OpenGLContext and make it look like they blend together, but I lose a bit of real estate that I do not want to give up if it can be avoided.

[Handoko]

The code I gave you is just the part for displaying the texture. The whole code I wrote was a complete class of OpenGL visual controls that I want to use in my game engine. It's still not fully finished but already tested and works correctly on both Linux and Windows.

My visual gl text component works like this:
On the constructor, it writes the string using TBitmap.TextOut to memory buffer. On the paint method, I use that code I gave you to call opengl functions to display the buffer (texture).

It is easy to find tutorials to show text using OpenGL, but unfortunately most of the codes are in C and C++. I managed to make it worked by trial and error.

I could put another panel next to the OpenGLContext and make it look like they blend together, but I lose a bit of real estate that I do not want to give up if it can be avoided.

Do you mean to overlap opengl layer with other visual component on the screen? It may work but sounds not easy and I don't think it is a good idea.

I have a bookmark that someone did opengl component. It has code to show text/font using opengl, which you can learn from his code. Here is the link:
http://forum.lazarus.freepascal.org/index.php/topic,29351.0.html

[Handoko]

... should not be affected by pan, zoom, rotate, etc.

It shouldn't be hard. You first write the text before calling any translation, scaling and rotation.

My testing on my gl visual controls, now already able to show static text with some other gl objects that are moving and scaling, but I haven't tested with rotation.

Can you show me the code you now already have?

[ehj666]

This picture shows what it looks like in the Delphi Windows application. The text at the top was just TLabels dropped on the canvas. The remainder is rendered through OpenGL. There is no OpenGL code to render the static text.

[Akira1364]

What is the canvas in your screenshot a part of? Just a form? The difference is TOpenGLControl is a standalone "TWinControl" descendant, with its own specific overridden paint procedure written with OpenGL in mind. It's not meant to have "normal" controls placed inside of it.

[lainz]

At least with the LCL. I don't know in delphi, but if you say in delphi works it can be.

I've developed some OpenGL controls, well hybrid controls (GL and LCL depending where you put them).

BGRAControlsFX:
https://github.com/bgrabitmap/bgracontrolsfx

Is not exactly text but there are buttons with text inside, so you can get the idea on how to make something similar.

[ehj666]

What is the canvas in your screenshot a part of? Just a form? The difference is TOpenGLControl is a standalone "TWinControl" descendant, with its own specific overridden paint procedure written with OpenGL in mind. It's not meant to have "normal" controls placed inside of it.

The canvas belongs to a TPanel. Here is part of the original code. First the initialization.

Code: Pascal  [Select][+][-]

1.   ScreenAspectRatio :=  GetSystemMetrics(SM_CXSCREEN) /
2.     GetSystemMetrics(SM_CYSCREEN);
3.   Application.OnException := ExceptionGL;
4.   pDC := GetDC(LivePlotPanel.Handle);
5.   CgDC := TCGDeviceContext.Create(pDC);
6.   CgDC.InitGL;
7.   glEnable(GL_DEPTH_TEST);
8.  

Then sizing the image to the frame.

Code: Pascal  [Select][+][-]

1. procedure TMainAppForm.SizeImage;
2.  
3.   var
4.     Range, AspectRatio: Extended;
5.  
6.   begin
7.     if Assigned(Pgm) then
8.       begin
9.       CgDC.MakeCurrent;
10.       glViewPort(0, 0, LivePlotPanel.Width, LivePlotPanel.Height);
11.       glMatrixMode(GL_PROJECTION);
12.       glLoadIdentity;
13.       AspectRatio := LivePlotPanel.Width / LivePlotPanel.Height;
14.       if LivePlotPanel.Width < LivePlotPanel.Height then
15.         begin
16.         Range := Pgm.XMax;
17.         glOrtho(-Range, Range, -Range / AspectRatio, Range / AspectRatio, -999999.0, 999999.0);
18.         end
19.       else
20.         begin
21.         Range := Pgm.YMax;
22.         glOrtho(-Range * AspectRatio, Range * AspectRatio, -Range, Range, -999999.0, 999999.0);
23.         end;
24.       glMatrixMode(GL_MODELVIEW);
25.       glLoadIdentity;
26.       LivePlotPanel.Invalidate;
27.       end;
28.   end;
29.  

The render then begins with:

Code: Pascal  [Select][+][-]

1.     CgDC.MakeCurrent;
2.     glClear(GL_COLOR_BUFFER_BIT or GL_DEPTH_BUFFER_BIT);
3.     glPushMatrix;
4.  

And ends with:

Code: Pascal  [Select][+][-]

1.     glMatrixMode(GL_MODELVIEW);
2.     glLoadIdentity;
3.     glEnd;
4.     glFlush;
5.     glPopMatrix;
6.     CgDC.PageFlip;
7.  

Of course if the OpenGLContext is not implemented like a TPanel then none of this really matters.

[Handoko]

Do you able to render text using OpenGL?

On your rendering routine, draw the text first before perform any tranformation, scaling and rotation.

[ehj666]

I don't do any of the text drawing in opengl, at least not in the original program.

I think I got it. I dropped a panel on the openglcontext, set the background colors to match, got rid of bevels, and then dropped labels on the panel.

[ehj666]

Not text related, but not worth starting a new thread. I am not getting anything to display on the glcontext. Here js the init and paint code basically copied from one of the examples:

Code: Pascal  [Select][+][-]

1. constructor TBackplot.Create(AGLControl: TopenGLControl);
2.  
3.   begin
4.     BackplotControl := AGLControl;
5.     with BackPlotControl do
6.        begin
7.        AutoResizeViewport := True;
8.        MultiSampling := 4;
9.        Invalidate;
10.        end;
11.   end;
12.  
13. procedure TBackplot.Paint;
14.  
15.   begin
16.      glClearColor(0.0, 0.0, 0.0, 1.0); //Set black background
17.      glClear(GL_COLOR_BUFFER_BIT or GL_DEPTH_BUFFER_BIT);
18.      glLoadIdentity;
19.      glBegin(GL_TRIANGLES);
20.        glColor3f(1, 0, 0);
21.        glVertex3f( 0.0, 1.0, 0.0);
22.        glColor3f(0, 1, 0);
23.        glVertex3f(-1.0,-1.0, 0.0);
24.        glColor3f(0, 0, 1);
25.        glVertex3f( 1.0,-1.0, 0.0);
26.      glEnd;
27.      BackplotControl.SwapBuffers;
28.   end;
29.  

It is clearly getting to glClearColor because the background is turning black (and I set a break point to prove it), but the triangle does not display. I am assuming that setting AutoSizeViewport puts whatever is rendered in the frame and scales appropriately.

What am I missing?

[Handoko]

The code works on my test. How did you use the code? Try this:

Code: [Select]

     glClearColor(0.0, 0.0, 0.0, 1.0); //Set black background
     glClear(GL_COLOR_BUFFER_BIT or GL_DEPTH_BUFFER_BIT);
     glLoadIdentity;
     glBegin(GL_TRIANGLES);
       glColor3f(1, 0, 0);
       glVertex3f( 0.0, 1.0, 0.0);
       glColor3f(0, 1, 0);
       glVertex3f(-1.0,-1.0, 0.0);
       glColor3f(0, 0, 1);
       glVertex3f( 1.0,-1.0, 0.0);
     glEnd;
     BackplotControl.SwapBuffers;
1. Start a new project: Lazarus main menu > File > New > Application.
2. Add GL in the uses clause.
3. Drop a TOpenGLControl to the form and resize it properly.
4. On the Object Inspector of OpenGLControl1, double click OnPaint event.
5. Drop the code there, but
6. Rename BackplotControl > OpenGLControl1.

Note:
I'm not sure what the code in the constructor for, so I simply ignore it.

And this is the result:

[ehj666]

Yep, that worked. So I went back to my project and removed the following from the constructor, and it worked too. That code was in the example I copied, so not sure what it is doing to prevent the triangle from displaying.

Code: Pascal  [Select][+][-]

1.        AutoResizeViewport := True;
2.        MultiSampling := 4;
3.        Invalidate;
4.  

[Handoko]

Hi, I've made the code with text and random moving/scaling rectangle. All using OpenGL. You can download the Test.zip to see the code.