Transform feedback example

[rogermc2]

This example currently produces:

V_Type: INTERLEAVED_ATTRIBS   V_Length:  2   Max Length:  0
Setup, Update_Program Link failed
ERROR: Could not find transform feedback binding for 'position_out.'
ERROR: Could not find transform feedback binding for 'velocity_out.'

An exception occurred in Main_Loop.Setup.
An exception occurred in Main_Loop.
An exception occurred in Transform_Feedback.
raised GL.ERRORS.INVALID_OPERATION_ERROR : gl-raise_exception_on_opengl_error.adb:10

I have left in debug Put_Line messages which would need to be removed eventually. I have commented out Get_Transform_Feedback_Varying associated code as this causes an exception on detecting Max Length: 0 associated with the V_Type attributes. This exception occurs prior to the Update_Program Link failed message being activated. I'll add the C version shortly after confirming that it still works.

[rogermc2]

Here is the C version code which has been built and run with Xcode 9.3. I hope its all there as the source is from a few different directories

As well as the graphic display, it reports:

GLFW Version: 3.3.0 Cocoa NSGL

Varying Max Length: 13
Varying Buffer mode: 8c8c

Varying name: position_out
Maximum name length: 12
Type of varying: 8b52
Size of varying: 1

Varying name: velocity_out
Maximum name length: 12
Type of varying: 8b51
Size of varying: 1

Varying Max Length: 13
Varying Buffer mode: 8c8c

Varying name: world_space_position
Maximum name length: 20
Type of varying: 8b52
Size of varying: 1
Program ended with exit code: 0.

transform_feedback.zip

[rogermc2]

I tried removing the link step removed from Program_From. The same failure messages occurred.

[rogermc2]

I think I had Transform_Feedback_Varyings working OK on another example.

[flyx]

Can you PR that other example?

[rogermc2]

Another similar example I checked produces the same problem. I was looking at a more complex example that uses Transform_Feedback_Varyings but couldn't complete compilation as GL.Objects.Buffers.Draw_Elements_Base_Vertex (glDrawElementsBaseVertex) seems to have disappeared from GL.Objects.Buffers.

[rogermc2]

I got the more complex example working by commenting out GL.Objects.Buffers.Draw_Elements_Base_Vertex

I don't think I can PR it as it contains quite a lot of new functionality including Assimp and ImageMagick routines. Also very much a work in progress, so probably a bit of a mess! This example that I'm trying to implement is from http://ogldev.atspace.co.uk/www/tutorial28/tutorial28.html The following initialisation code seems to link the varyings OK as it generates the PS_Update_Technique.Init, Update_Program Link for Varyings ok message.

procedure Init (theTechnique : in out Update_Technique) is
      use GL.Objects.Programs;
      use GL.Objects.Shaders;
      use Program_Loader;
      Varyings       : constant String := "Type1,Position1,Velocity1,Age1";
      OK             : Boolean;
   begin
      --  Program_From includes linking
      theTechnique.Update_Program := Program_From
        ((Src ("src/shaders/ps_update.vs", Vertex_Shader),
         Src ("src/shaders/ps_update.gs", Geometry_Shader),
         Src ("src/shaders/ps_update.fs", Fragment_Shader)));

      OK := GL.Objects.Programs.Link_Status (theTechnique.Update_Program);
      if not OK then
         Put_Line ("PS_Update_Technique.Init, Update_Program Link failed");
         Put_Line (GL.Objects.Programs.Info_Log (theTechnique.Update_Program));
      else
         Put_Line ("PS_Update_Technique.Init, Update_Program Link ok");
      end if;

      Use_Program (theTechnique.Update_Program);
      Transform_Feedback_Varyings (theTechnique.Update_Program, Varyings,
                                   Interleaved_Attribs);
      theTechnique.Update_Program.Link;
      OK := GL.Objects.Programs.Link_Status (theTechnique.Update_Program);
      if not OK then
         Put_Line ("PS_Update_Technique.Init, Update_Program Link for Varyings failed");
         Put_Line (GL.Objects.Programs.Info_Log (theTechnique.Update_Program));
      else
         Put_Line ("PS_Update_Technique.Init, Update_Program Link for Varyings ok");
      end if;

      Utilities.Set_Uniform_Location (theTechnique.Update_Program, "gDeltaTimeMillis",
                                      theTechnique.Delta_Millisec_Location);
      Utilities.Set_Uniform_Location (theTechnique.Update_Program, "gRandomTexture",
                                      theTechnique.Random_Texture_Location);
      Utilities.Set_Uniform_Location (theTechnique.Update_Program, "gTime",
                                      theTechnique.Time_Location);
      Utilities.Set_Uniform_Location (theTechnique.Update_Program, "gLauncherLifetime",
                                      theTechnique.Launcher_Lifetime_Location);
      Utilities.Set_Uniform_Location (theTechnique.Update_Program, "gShellLifetime",
                                      theTechnique.Shell_Lifetime_Location);
      Utilities.Set_Uniform_Location (theTechnique.Update_Program, "gSecondaryShellLifetime",
                                      theTechnique.Secondary_Shell_Lifetime_Location);
   exception
      when  others =>
         Put_Line ("An exception occurred in PS_Update_Technique.Init.");
         raise;
   end Init;

[rogermc2]

I'm writing a short varyings test program based on the Init procedure to test transform varyings which I can PR when completed.

[rogermc2]

I added some tests:

      V_Size := Transform_Feedback_Varyings (Update_Program);
      V_Max_Length := Transform_Feedback_Varying_Max_Length (Update_Program);
      V_Type := Transform_Feedback_Buffer_Mode (Update_Program);
      Put_Line ("Transform_Feedback_Buffer_Mode: " & Buffer_Mode'Image (V_Type));
      Put_Line ("Transform_Feedback_Size: " & Size'Image (V_Size));
      Put_Line ("Transform_Feedback_Max_Length: " & Size'Image (V_Max_Length));

This seems to produce correct results, at least for Mode and Size:

Transform_Feedback_Buffer_Mode: INTERLEAVED_ATTRIBS
Transform_Feedback_Size:  4
Transform_Feedback_Max_Length:  10

I also tried Get_Transform_Feedback_Varying but it failed because some parameters need to be declared out. I'll have a go at fixing this next. Also, Transform_Feedback_Varyings doesn't seem to correspond to the glTransformFeedbackVaryings specification. I'll investigate this later.

[rogermc2]

I added some tests:

      V_Size := Transform_Feedback_Varyings (Update_Program);
      V_Max_Length := Transform_Feedback_Varying_Max_Length (Update_Program);
      V_Type := Transform_Feedback_Buffer_Mode (Update_Program);
      Put_Line ("Transform_Feedback_Buffer_Mode: " & Buffer_Mode'Image (V_Type));
      Put_Line ("Transform_Feedback_Size: " & Size'Image (V_Size));
      Put_Line ("Transform_Feedback_Max_Length: " & Size'Image (V_Max_Length));

This seems to produce correct results, at least for Mode and Size:

Transform_Feedback_Buffer_Mode: INTERLEAVED_ATTRIBS
Transform_Feedback_Size:  4
Transform_Feedback_Max_Length:  10

I also tried Get_Transform_Feedback_Varying but it failed because some parameters need to be declared out. Also, Transform_Feedback_Varyings doesn't seem to correspond to glTransformFeedbackVaryings I'll have a go at fixing this next.

[rogermc2]

Changed Transform_Feedback_Varyings to Transform_Feedback_Varyings_Size as it doesn't call glTransformFeedbackVaryings but actually returns Program_Size_Param (Object, Enums.Transform_Feedback_Varyings)

[flyx]

I'll have a look at this somewhen in the next week.

[rogermc2]

Weird result! Varyings : constant String := "Type1,Position1,Velocity1,Age1"; is accepted. But if I delete "1" from any of the names, it fails. For example, Velocity instead of Velocity1 produces: Update_Program Link for Varyings failed ERROR: Could not find transform feedback binding for 'Velocity.'

[rogermc2]

I have Get_Transform_Feedback_Varying working.

     GL.Objects.Programs.Get_Transform_Feedback_Varying
        (Update_Program, 0, Buffer_Size, Name_Length, Vertices_Length, V_Type, Varyings_Name);
      Put_Line ("Varying name: " & Varyings_Name (1 .. Integer (Name_Length)));

etc. produces:

Varying name: Type1
Varying name: Position1
Varying name: Velocity1
Varying name: Age1

I've PR'd the test program in case it helps.

[rogermc2]

Transform feedback example now runs OK after changing varying names to end with "1": ` Varyings : constant String := "position1,velocity1"; Yet to test fully.

Cosmetic problem: Space missing in Set_Vertex_Attrib_Pointer error message: Use the otherSet_Vertex_Attrib_Pointer, Set_Vertex_Integer_Attrib_Pointer ...

[rogermc2]

Transform feedback example now runs OK. Ready to merge?