Thanks for the advice everyone. I'm using Haskell rather than C/C++ because I'm not particularly interested in writing an entire application in C/C++. If I learn OpenGL using C, then I'm still going to have to learn to use the bindings in whatever language I ultimately decide to use. Haskell seems well suited to this given all of its nice foreign interface packages. Additionally, knowing how to interface with C libraries seems like a useful skill to have. I've already gone through the first few chapters of the red book using the higher level OpenGL. The concern that lead me to try OpenGLRaw instead is that drawing every vertex/color/etc with a separate function call seems incredibly inefficient. I imagine I'm going to have to learn to use buffers at some point. In fact, there is a section about them in the second chapter of the red book, which I skipped because I couldn't figure out how to do it with the high level OpenGL package. Also, it seems like the high level package only truly supports the 2.1 spec, whereas the Raw package supports the 3.2 spec. If everyone legitimately thinks that the higher level library is the way to go for writing actual OpenGL programs then I'll give it another shot. It looks like the Haskell translations of the red book examples might get me unblocked in that respect. I just felt like I would be better served by learning how to use the lower level bindings, which are closer to actual OpenGL. On Mon, Mar 11, 2013 at 6:43 AM, Ertugrul Söylemez wrote:

Michael Baker wrote:

...

However, I'm struggling a bit because I haven't used Haskell's foreign interface before. Here is an attempt which is expected to draw a triangle, but instead draws nothing: http://hpaste.org/83837

The first thing I notice is that you never set a vertex color, which is black by default in all cases I've encountered. So it may be drawing, but you may simply not see it. =)

Before you begin drawing put this somewhere:

glColor3f 1 0 0

That should draw a red shape. Another option is to set a different clear color:

glClearColor 1 0 0 1

That sets a red background.

...

Does anyone know of a tutorial for OpenGLRaw or the foreign interface that might help me understand how to marshall data around? It seems like many people turn to OpenGLRaw when they're learning OpenGL so that they can follow the tutorials. I imagine it would be useful to have a guide out there that covers how to actually use it.

My recommendation is to go with the higher level OpenGL library. The main difference is that the `gl` prefix is dropped and the numerous similar functions (`color2f`, `color3f`, `color4f`, etc.) are collapsed into a single polymorphic function `color`:

import qualified Graphics.Rendering.OpenGL as GL

GL.color (GL.Color3 1 0 (0 :: GL.GLfloat))

This looks more complicated, but it makes other things a lot easier, so in the end you win.

Greets, Ertugrul

-- Not to be or to be and (not to be or to be and (not to be or to be and (not to be or to be and ... that is the list monad.

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Excellent Isaac, thanks! On Mon, Mar 11, 2013 at 12:37 PM, Isaac Dupree < ml@isaac.cedarswampstudios.org> wrote:

On 03/11/2013 11:41 AM, Michael Baker wrote:

...

The concern that lead me to try OpenGLRaw instead is that drawing every vertex/color/etc with a separate function call seems incredibly inefficient. I imagine I'm going to have to learn to use buffers at some point.

You are correct. Partly for that reason, glBegin()/glEnd()/glVertex*() don't even exist in OpenGL ES and are deprecated since OpenGL 3.0. It's a shame that so many OpenGL tutorials still teach them.

Note to others: your program depends on glfw-b (or anyway, Hackage 'glfw-b' works and Hackage 'glfw' doesn't).

glEnableVertexAttribArray/**glVertexAttribPointer are for passing data to shader programs, I believe. Everyone should use shader programs (GLSL). GL without shader programs uses the "fixed-function pipeline" which is deprecated. But I haven't used shaders yet, so I've attached how to do it with VBOs and the fixed-function pipeline. I used glInterleavedArrays and glDrawArrays. (That's probably not the only way to do it; OpenGL has lots of legacy and semi-redundant functions.)

As jean verdier noted, your byte count argument to glBufferData was wrong; "fromIntegral $ length verticies * sizeOf (head verticies)" fixes it.

Four coordinates per vertex is (as far as I know) not very useful for two-dimensional or three-dimensional shapes.

Doing glGenBuffers every frame without glDeleteBuffers leaks buffers. Either save them or delete them. I didn't fix this. Control.Exception's bracket or bracket_ can be useful for this sort of thing.

I also attached a version that can attach a color to each vertex. Haskell FFI peeps, is there a better way to do this than writing a Storable instance for each GL buffer data layout?

-Isaac (who has been learning modern OpenGL for http://www.lasercake.net/)

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