Re: [fpc-pascal] OpenGL and SDL frustrations

[Ryan Joseph]

> On May 26, 2017, at 11:56 AM, nore...@z505.com wrote:
> 
> All these calls look kind of tedious, instead of using a wrapper. But maybe 
> you want to learn opengl at its heart and not use a wrapper.. and learn all 
> the fine details the hard way (full respect for that).

Imo I think it pays off to learn the actual graphics pipeline and what the 
process is really doing from direct memory in CPU to GPU. Graphics are so 
sensitive to performance and minor optimizations it would no doubt bother me 
deep down inside if I didn’t have 100% control over the process. Overall it’s 
only a minor part of the code actually so once you get it down it can be buried 
and not worried about later.

Regards,
Ryan Joseph

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Re: [fpc-pascal] OpenGL and SDL frustrations

[Ryan Joseph]

> On May 25, 2017, at 7:02 PM, Anthony Walter  wrote:
> 
> Ryan,
> 
> Are you loading the OpenGL API functions using SDL_GL_GetProcAddress? You 
> really should be doing that or you're asking for problems.
> 
> Anyways, if you want maximum capability you should probably use ES version 2, 
> as it's supported on the most devices. It requires you to drop the fixed 
> function pipeline, that is dropping glBegin/glEnd and using GLSL vertex and 
> fragment shaders. It's mostly like OpenGL 2.0, with a few differences, like 
> there is no glMatrixMode.
> 

I loaded the functions using Load_GL_VERSION_3_3 (and similar) from the Free 
Pascal RTL and it seems to correctly load the functions.

Right now I’m using 2.1 and the fixed pipeline because I don’t really need 
shaders but I’m learning shaders and matrix transforms now so if there’s any 
performance benefit I can update my code base.

Regards,
Ryan Joseph

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Re: [fpc-pascal] OpenGL and SDL frustrations

[noreply]

On 2017-05-23 22:13, Ryan Joseph wrote:

I’ve wasted so much time on this I just need to stop and ask for help
already. Over the last few years I’ve been picking away at OpenGL and
only ever got the legacy 2.x API to work which has been fine for
making 2D games but I wanted to at least learn the modern API and
shaders.


Not sure what ZenGL uses for opengl version but why do you struggle to 
use opengl directly instead of using a wrapper like zengl that has 
already made the functions available for you...


The only problem with using a wrapper like zengl or andorra is that of 
course it could go stale and not be updated, I'm not even sure if it 
uses 2.x, I have forgotten.


[...]

if SDL_Init(SDL_INIT_VIDEO) < 0 then
Fatal('SDL could not initialize! '+SDL_GetError);

// load function pointers
if Load_GL_VERSION_3_3 = false then
Fatal('OpenGL is not loaded');

SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, 
SDL_GL_CONTEXT_PROFILE_CORE);

// NOTE: 4.0 doesn't work, GL_VERSION return null
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 3);
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 16);



All these calls look kind of tedious, instead of using a wrapper. But 
maybe you want to learn opengl at its heart and not use a wrapper.. and 
learn all the fine details the hard way (full respect for that).

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Re: [fpc-pascal] OpenGL and SDL frustrations

[Marco van de Voort]

In our previous episode, Anthony Walter said:
> And if you're not using GLSL shaders, then you don't need anything greater
> than Open 1.5. You can see the list of changes at the link below. With the
> exception of frame buffer objects (better known as render to texture) in
> version 3.0 and up, there's likely very little you're going to need in the
> 3.0+ realm of APIs you're ever going to need.
> 
> https://www.khronos.org/opengl/wiki/History_of_OpenGL#Summary_of_version_changes

PBO speeds up texture upload on most DX10+ cards. 
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Re: [fpc-pascal] OpenGL and SDL frustrations

[Anthony Walter]

Ryan,

Are you loading the OpenGL API functions using SDL_GL_GetProcAddress? You
really should be doing that or you're asking for problems.

Anyways, if you want maximum capability you should probably use ES version
2, as it's supported on the most devices. It requires you to drop the fixed
function pipeline, that is dropping glBegin/glEnd and using GLSL vertex and
fragment shaders. It's mostly like OpenGL 2.0, with a few differences, like
there is no glMatrixMode.

And if you're not using GLSL shaders, then you don't need anything greater
than Open 1.5. You can see the list of changes at the link below. With the
exception of frame buffer objects (better known as render to texture) in
version 3.0 and up, there's likely very little you're going to need in the
3.0+ realm of APIs you're ever going to need.

https://www.khronos.org/opengl/wiki/History_of_OpenGL#Summary_of_version_changes
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Re: [fpc-pascal] OpenGL and SDL frustrations

[Ryan Joseph]

> On May 25, 2017, at 2:30 PM, Anthony Walter  wrote:
> 
> You need to tell SDL what OpenGL kind and version before you create a window. 
> For example if you want OpenGLES 2.0 you would write:
> 
>   SDL_Init(SDL_INIT_VIDEO);
>   SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, 
> SDL_GL_CONTEXT_PROFILE_ES);
>   SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 2);
>   SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);
>   
> If you want normal OpenGL 4.0 you would write:
> 
>   SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, 
> SDL_GL_CONTEXT_PROFILE_CORE);
>   SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 4);
>   SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);
> 

That’s just a hint to SDL but it doesn’t guarantee anything. See my example 
below where I asked for 3.3 but got 4.1. I learned I can use a lower version of 
GLSL so I can enforce that version but for OpenGL I’m stuck on 4.1 or 2.1, at 
least on my Mac. That wouldn’t be a problem I guess but I’m trying to follow 
tutorials which have subtle things not work but I’m not using the same version 
as them. Maybe it doesn’t matter though and 4.1 will run on older graphics 
cards? No idea but it’s worrying.

Regards,
Ryan Joseph

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Re: [fpc-pascal] OpenGL and SDL frustrations

[Anthony Walter]

Oh and another note, you cannot load your gl function such as (glClear in
my previous reply, this time I use glGenTextures):

var glGenTextures: procedure(n: GLsizei; var textures: GLuint); cdecl;

Until you create and make current your OpenGL context.
SDL_GL_MakeCurrent(window, context); // after this is done the first time
you can then load the OpenGL functions matching your requested version

So the order is

SDL_Init()
SDL_GL_SetAttribute() multiple times
SDL_CreateWindow() returns your window
SDL_GL_CreateContext() returns your context
SDL_GL_MakeCurrent() makes gl functions available
SDL_GL_GetProcAddress() for every gl function in your requested version

Then you are done initializing everything and can write a
game/demo/whatever thing you want.
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Re: [fpc-pascal] OpenGL and SDL frustrations

[Anthony Walter]

You need to tell SDL what OpenGL kind and version before you create a
window. For example if you want OpenGLES 2.0 you would write:

SDL_Init(SDL_INIT_VIDEO);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_ES);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 2);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);
If you want normal OpenGL 4.0 you would write:

SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK,
SDL_GL_CONTEXT_PROFILE_CORE);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 4);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);

Then you can create the SDL and load the appropriate OpenGL function
prototypes using:

glClear := SDL_GL_GetProcAddress('glClear');
It's up to you to know which functions are part of which which OpenGL spec,
and you should need to load the functions dynamically to stubs:

var glClear: procedure(mask: GLbitfield); cdecl;
Don't forget, if you want a specific values for stencil bits, pixel order,
multisampling levels and other stuff, you need to set those values before
you create a window. Check the return values of SDL_CreateWindow and
SDL_GL_CreateContext to see if anything above fails, for example the target
device doesn't support OpenGL 4.0.

SDL_GL_SetAttribute(SDL_GL_MULTISAMPLESAMPLES, 8); // 8x anti-aliasing,
must be called before SDL_CreateWindow
SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 16); // 16 bit stencil buffer,
must be called before SDL_CreateWindow
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Re: [fpc-pascal] OpenGL and SDL frustrations

[Ryan Joseph]

> On May 24, 2017, at 7:18 PM, Graeme Geldenhuys 
>  wrote:
> 
>> Any ideas on what’s wrong with this?
> 

Ok, I got an answer from a person on YouTube and figured this out.

The problem was 1) that SDL is returning a different version then I asked for 
and I didn’t do proper error checking. glEnableVertexAttribArray was failing 
for example because with OpenGL 4.1 (or earlier) a VAO is required before using 
VBO’s and 2) again, since 4.x, a shader is required to even draw white 
triangle. The demos I saw must have been on some version of 3.x but I was on 
4.1.

I’m still now sure how to guarantee SDL returns the version I want and it looks 
in your code you didn’t even try to specify anything besides core 
compatibility, not that it makes any difference because I always get 4.1 on my 
Mac or 2.1 and GLSL 1.2 for legacy mode. This begs the question of how I can 
write shaders if on any given computer I get a different version of GLSL.

At least I got it working FINALLY after so much hassle but everything I do 
could easily break on others computers so...

Regards,
Ryan Joseph

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Re: [fpc-pascal] OpenGL and SDL frustrations

[Graeme Geldenhuys]

On 2017-05-24 04:13, Ryan Joseph wrote:


Any ideas on what’s wrong with this?


I actually used the Java + OpenGL tutorials on YouTube, and translating 
those examples to Object Pascal + OpenGL + SDL2 was pretty easy.


This is my favourite one, and uses "modern OpenGL" only.


https://www.youtube.com/watch?v=VS8wlS9hF8E=PLRIWtICgwaX0u7Rf9zkZhLoLuZVfUksDP

  "OpenGL 3D Game Tutorial" by ThinMatrix.

I also wanted something reusable, so I implemented classes in separate 
units that I can reuse between projects. Instead of 100's of loosely 
scattered OpenGL API calls. I was actually going to contribute all this 
work as part of my Lazarus Graphics Programming Contest entry, but I 
might just release it earlier than that.


Anyway, attached is one such unit setting up my display. I use 
proprietary NVIDIA drivers under FreeBSD, and I only target OpenGL 4.x 
with my code. It works perfectly here.


My program code is pretty much like this:

   TDisplayManager.CreateDisplay;

   while running do
   begin
 // do the "gaming loop" here
 TDisplayManager.UpdateDisplay;
   end;

   // clean-up code here
   TDisplayManager.CloseDisplay;



Regards,
  Graeme

--
fpGUI Toolkit - a cross-platform GUI toolkit using Free Pascal
http://fpgui.sourceforge.net/

My public PGP key:  http://tinyurl.com/graeme-pgp
unit DisplayManager;

{$mode objfpc}{$H+}

interface

uses
  SDL2,
  GL,
  GLext;

type

  TDisplayManager = class(TObject)
  private
class var FSDLWindow: PSDL_Window;
class var FSDLGLContext: TSDL_GLContext;
const
  cWIDTH = 856;
  cHEIGHT = 480;
  public
class procedure CreateDisplay; static;
class procedure UpdateDisplay; static;
class procedure CloseDisplay; static;
//property  SDLWindow: PSDL_Window read FSDLWindow;
  end;

implementation

{ TDisplayManager }

class procedure TDisplayManager.CreateDisplay;
begin
  if SDL_Init(SDL_INIT_VIDEO) < 0 then
HALT;

  // setting so that deprecated functions are disabled
  SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);

  //get an OpenGL window and create OpenGL context
  FSDLWindow := SDL_CreateWindow('OpenGL Game Tutorial', SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, cWIDTH, cHEIGHT, SDL_WINDOW_OPENGL);
  if FSDLWindow = nil then
HALT;

  FSDLGLContext := SDL_GL_CreateContext(FSDLWindow);
  if FSDLGLContext = nil then
HALT;

  //init OpenGL and load extensions
  if Load_GL_VERSION_4_0 = false then
if Load_GL_VERSION_3_3 = false then
  if Load_GL_VERSION_3_2 = false then
//if Load_GL_VERSION_3_0 = false then
begin
  writeln(' ERROR: OpenGL 3.2 or higher needed. ');
  HALT;
end;

  glViewport(0, 0, cWIDTH, cHEIGHT);

  //print out OpenGL vendor, version and shader version
  writeln( 'Vendor: ' + glGetString( GL_VENDOR ) );
  writeln( 'OpenGL Version: ' + glGetString( GL_VERSION ) );
  writeln( 'Shader Version: ' + glGetString( GL_SHADING_LANGUAGE_VERSION ) );
end;

class procedure TDisplayManager.UpdateDisplay;
begin
  SDL_GL_SwapWindow(FSDLWindow);
end;

class procedure TDisplayManager.CloseDisplay;
begin
  SDL_GL_DeleteContext(FSDLGLContext);
  SDL_DestroyWindow(FSDLWindow);
  SDL_Quit;
end;

end.

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[fpc-pascal] OpenGL and SDL frustrations

[Ryan Joseph]

I’ve wasted so much time on this I just need to stop and ask for help already. 
Over the last few years I’ve been picking away at OpenGL and only ever got the 
legacy 2.x API to work which has been fine for making 2D games but I wanted to 
at least learn the modern API and shaders.

Here’s a snippet I cobbled together from a test program. It merely wants to 
draw a triangle. The actual OpenGL is from a tutorial and I don’t see how 
anything could be simpler than this. The only thing curious to me is why I 
can’t load the version of OpenGL I want from SDL. If I attempt to load 4.0 
(with SDL_GL_SetAttribute) GL_VERSION returns null but if I load 3.3 it works 
and GL_VERSION returns 4.1 anyways (I’m a Mac from 2015).

I removed the error handling code here but I don’t get any errors, just a black 
screen. Despite the tutorial I was following not using a shader they still got 
a white triangle (I added a shader also but it still didn’t work so I removed 
it to reduce complexity). The only thing I can think of is they were using GLEW 
and it did some init that SDL isn’t doing but I doubt it. This is barebones 
simple OpenGL here.

Any ideas on what’s wrong with this? I don’t care about this example in 
particular I just want to draw ANYTHING using OpenGL 3.3 so I can move forward.

=

type
TVec2 = record
x, y: GLfloat;
end;

var
verts: array[0..2] of TVec2;
bufferID: GLuint;   
vao: GLuint;

// run sdl window
if SDL_Init(SDL_INIT_VIDEO) < 0 then
Fatal('SDL could not initialize! '+SDL_GetError);

// load function pointers
if Load_GL_VERSION_3_3 = false then
Fatal('OpenGL is not loaded');

SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
// NOTE: 4.0 doesn't work, GL_VERSION return null
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 3);   
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 16);

// create window
window := SDL_CreateWindow('SDL Tutorial', SDL_WINDOWPOS_UNDEFINED, 
SDL_WINDOWPOS_UNDEFINED, width, height, SDL_WINDOW_SHOWN + SDL_WINDOW_OPENGL);
context := SDL_GL_CreateContext(window);
SDL_GL_MakeCurrent(window, context);
SDL_GL_SetSwapInterval(1);

writeln('Vendor: ', glGetString(GL_VENDOR));
writeln('OpenGL Version: ', glGetString(GL_VERSION));
writeln('GLSL Version: ', glGetString(GL_SHADING_LANGUAGE_VERSION));

// NOTE: despite SDL_GL_SetAttribute asking for 3.3 and 4.0 failing GL_VERSION 
still returns 4.1
// Vendor: Intel Inc.
// OpenGL Version: 4.1 INTEL-10.25.13
// GLSL Version: 4.10 

// setup
glViewPort(0, 0, width, height);

// simplest example possible
// https://www.youtube.com/watch?v=Dyue3MzJDss
verts[0].x := 0.0;
verts[0].y := 1.0; 
verts[1].x := -1.0;
verts[1].y := -1.0; 
verts[2].x := 1.0;
verts[2].y := -1.0;

// NOTE: glEnableVertexAttribArray returns an error if I don't bind a vao
glGenVertexArrays(1, @vao);
glBindVertexArray(vao);

// gen array buffer and bind to verts
glGenBuffers(1, @bufferID);
glBindBuffer(GL_ARRAY_BUFFER, bufferID);
glBufferData(GL_ARRAY_BUFFER, sizeof(verts), @verts, GL_STATIC_DRAW);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(TVec2), nil);

// draw loop
glClearColor(0, 0, 0, 1);
glClear(GL_COLOR_BUFFER_BIT);
glDrawArrays(GL_TRIANGLES, 0, 3);
SDL_GL_SwapWindow(window);
...


Regards,
Ryan Joseph

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