I am attempting to create an OpenGL context with osmesa (off-screen mesa). I wish to use the software implementation of mesa without a window and save the rendered output to a png file.
http://www.mesa3d.org/osmesa.html
I create a GL context with the following:
OSMesaContext context = OSMesaCreateContext(GL_RGBA, NULL);
OSMesaMakeCurrent(context, buffer, GL_UNSIGNED_BYTE, width, height);
However, when I invoke glGetString(GL_VERSION) the version is 2.1 Mesa 10.1.1. As expected, none of my GLSL ES shaders compile. When using SDL I can supply a version hint and create a GLES 2.0 context.
How do I specify the version of the GL context being created by osmesa?
If you look at src/mesa/drivers/osmesa/osmesa.c, around line 745, you can see that it explicitly asks for an OpenGL compatibility profile, which Mesa limits to OpenGL 2.1 and GLSL 130 (see src/mesa/main/version.c line . Replacing API_OPENGL_COMPAT with API_OPENGL_CORE results with the OpenGL version being 0.0 in Mesa 10.6.2, so unfortunately, the simple fix doesn't work. But, setting the MESA_GL_VERSION_OVERRIDE environment variable to "3.3" appears to work. Haven't tested beyond seeing what glGetString(GL_VERSION) returns. Good luck!
Related
I am writing a plugin on Maya/MacOS which is compiling a vertex shader for OpenGL:
const char* vscode =
{
"#version 150\n"
...
}
However executing the code in Maya gives me
ERROR: 0:1: '' : version '150' is not supported
The OpenGL version returned is 2.1 ATI-1.42.6. I tried to change the OpenGL via glut
glutInitDisplayMode(GLUT_3_2_CORE_PROFILE);
But it does not seem to change the OpenGL Core Profile. How can I change the core profile from within a Maya plugin, or how can I know which "xxx" version would be supported in the shader ?
The OpenGL version returned is 2.1 ATI-1.42.6. I tried to change the OpenGL via glut
Does Maya use GLUT? No! So how so you expect this to work then?
GLUT is a independent library that does window and OpenGL context creation. GLUT is not part of OpenGL and GLUT can not influence OpenGL context management of programs not using GLUT.
Maya does its OpenGL context management internally and when your plugin is called a OpenGL context is already created and the version profile of that particular context set into stone.
But what you can do is you can create a very own OpenGL context, just for your plugin and connect it with the OpenGL context that Maya created (OpenGL context sharing). Doing this is advisable anyway, since this separates OpenGL your plugin uses from OpenGL state Maya uses.
You will have to use the system level OpenGL context management APIs for that. So no GLUT, no GLFW, no SMFL or other helper libraries. Don't worry, it's not too difficult to do. Regarding connecting with the OpenGL context of Maya, every OpenGL context management API has functions to query the currently active OpenGL context and the drawable it's active on. Use those to store which context+drawable pair was active before your plugin got called, then before returning to Maya reset the OpenGL context activation to that pair.
So, I googled a lot of opengl 3.+ tutorials, all incorporating shaders (GLSL 330 core). I however do not have a graphics card supporting these newer GLSL implementations, either I have to update my driver but still I'm not sure if my card is intrinsically able to support it.
Currently my openGL version is 3.1, and I created on windows with C++ a modern context with backwards compatibility. My GLSL version is 1.30 via NVIDIA Cg compiler (full definition), and GLSL 1.30 -> version 130.
The problem is : version 130 is fully based on the legacy opengl pipeline, because it contains things like viewmatrix, modelmatrix, etc. Then how am I supposed to use them when I am using core functions in my client app (OpenGL 3+)?
This is really confusing, give me concrete examples.
Furthermore, I want my app to be able to run on most OpenGL implementations, then could you tell me where the border is between legacy GLSL and modern GLSL? Is GLSL 300 the modern GLSL, and is there a compatibilty with OpenGL 3.+ with older GLSL versions?
I would say OpenGL 3.1 is modern OpenGL.
Any hardware that supports OpenGL 3.1 is capable of supporting OpenGL 3.3. Whether the driver always support of it is another matter. Updating your graphics card will probably bump you up to OpenGL 3.3.
Just to clear this up OpenGL 3.1 is not legacy OpenGL.
legacy OpenGL would be:
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glRotatef(90.0, 0.0, 1.0, 0.0);
glTranslatef(0.0, 0.0, -5.0);
Which OpenGL 3.1 with a compatibility context supports, but that doesn't mean it should be used. If you are developing for OpenGL 3 capable hardware you should most definitely not be using it. You can disable the legacy functionality by requesting a core context.
if you are using shaders then you already moved away the legacy fixed function pipeline. So GLSL 130 is not legacy :P.
Working on my Linux Laptop with my Intel CPU where the latest stable drivers are only at OpenGL 3.1 (Yes OpenGL 3.3 commits are in place, but I'm waiting for MESA 10 ;) ) I have without much effort been able to get the OpenGL 3.3 Tutorials to run on my machine without touching legacy OpenGL.
One of the wonderful things about OpenGL is that you can extend the functionality with OpenGL extension. Even if your HW isn't capable of handling OpenGL 4.4 you can still use the extensions that doesn't require OpenGL 4 HW with updated drivers!
See https://developer.nvidia.com/opengl-driver and http://developer.amd.com/resources/documentation-articles/opengl-zone/ for info on what features are added to older HW, but if you are uncertain all you have to do is test it on your HW.
And I'll finish of by saying Legacy OpenGL also has it's place.
In my opinion legacy OpenGL might be easier to learn than modern OpenGL, since you don't need knowledge of shaders and OpenGL buffers to draw your first triangle, but I don't think you should be using it in a modern production application.
If you need support for old hardware you might need to use an older OpenGL version. Even modern CPU's support OpenGL 3 so I would not worry about this to much.
Converting from OpenGL 3.3 to OpenGL 3.0
I tested it on the tutorials from http://www.opengl-tutorial.org/. I cannot put the code up I converted as most of it is as is from the tutorials and I don't have permission to put the code here.
They author talked about OpenGL 3.1, but since he is capped at glsl 130 (OpenGL 3.0) I am converting to 3.0.
First of all change the context version to OpenGL 3.0 (Just change
the minor version to 0 if your working from the tutorials). Also don't set it to use core context if your using OpenGL 3.0 since as far as I know ARB_compatibility is only available from OpenGL 3.1.
Change the shader version to
#version 130
Remove all layout binding in shaders
layout(location = #) in vec2 #myVarName;
to
in vec2 #myVarName;
Use glBindAttribLocation to bind the in layouts as they were specified (see 3)
e.g
glBindAttribLocation(#myProgramName, #, "#myVarName");
Use glBindFragDataLocation to bind the out layout as they were specified (see 3)
e.g
glBindFragDataLocation(#myProgramName, #, "#myVarName");
glFramebufferTexture doesn't work in OpenGL 3.0. (Used for shadowmapping and deferred rendering etc.). Instead you need to use glFramebufferTexture2D. (It has a extra parameter, but the documentation is sufficient)
Here is screenshot of tutorial16 (I though this one covered the most areas and used this a test to see if that all that's needed)
There is a mistake in the source of tutorial16 (At the time of writing). The FBO is set to have no color output, but the fragment shader still outputs a color value, causing a segfault (Trying to write to nothing ussually does that). Simply changing the depth fragment shader to output nothing fixes it. (Doesn't produce segfault on more tolerant drivers, but that's not something you should bargain on)
I'm going to start implementing OpenGL 3 into my application. I currently am using OpenGL 1.1 but I wanted to keep some of it due to problems if I attempt to change the code but I wanted to change some of my drawing code to a faster version of OpenGL. If I do things like bind textures in OpenGL 1.1 can I draw the texture in OpenGL 3?
Mixing OpenGL versions isn't as easy as it used to be. In OpenGL 3.0, a lot of the old features were marked as "deprecated" and were removed in 3.1. However, since OpenGL 3.2, there are two profiles defined: Core and Compatibility. The OpenGL context is created with respect to such a profile. In compatibility profile,
all the deprecated (and in core profiles removed) stuff is still availbale, and it can be mixed as well. You can even mix a custom vertex shader with the fixed-function fragment processing or vice versa.
The problem here is that it is not grequired that implementors actually provide support for the compatibility profile. On MacOS X, OpenGL 3.x and 4.x are supported in core profile only.
In you specific example, binding textures will work in all cases, since that funtctionality exists unmodified in all versions from 1.1 to 4.3 (and is likely to do so in the near future). However, most of your drawing calls are likely to be not available in the newer core profiles.
Omg.. opengl 1.1 is from 1997! Do yourself a favor and get rid of the fixed-function pipeline stuff and adapt to OpenGL 4.x. However, you can try
#version 420 core
in your shader.
I 'd like to render a CALayer into my openGL Context in openGL 3.2 Core.
I'm using CARenderer to render the layer but when I try to render I get the following error.
CoreAnimation: unsupported graphics hardware; need two or more texture units; need ARB_texture_rectangle extension; need EXT_framebuffer_object extension; need ARB shader extensions.
The problem doesn't occur when I ask for the legacy version of openGL. Is there a constant to pass to CARenderer in the rendererWithCGLContext:options: ?
I've been trying to work with OpenGL ES 2 in Android for some time now, but I'm finding the lack of experience with OpenGL itself to be an issue, since I barely understand what all the GLES20 methods actually do. I've decided to try to learn actual OpenGL, but a little bit of reading has informed me that each version of OpenGL is drastically different from its predecessor. Wikipedia isn't very clear on which version that OpenGL ES2 most closely resembles.
So, my question is, which version of OpenGL should I learn for the purpose of better understanding OpenGL ES2?
According to the book OpenGL ES 2.0 Programming Guide:
The OpenGL ES 1.0 and 1.1 specifications implement a fixed function
pipeline and are derived from the OpenGL 1.3 and 1.5 specifications,
respectively. The OpenGL ES 2.0 specification implements a
programmable graphics pipeline and is derived from the OpenGL 2.0
specification.
OpenGL ES 2.0’s closest relative is OpenGL 2.0. Khronos provides a difference specification, which enumerates what desktop OpenGL functionality was removed to create OpenGL 2.0. The shading language for OpenGL ES 2.0 (GLSL ES 1.0) is derived from GLSL 1.20.
OpenGL ES2.0 is almost one-to-one copy of WebGL.
The differences are practically only in the setup of the environment, which in Android happens with EGL and which happens in WebGL with calls to DOM methods. (setting canvas)
The comparison to "open gl" is next to impossible, as Open GL means almost fixed and hidden rendering pipeline, which is controlled by stack of matrices and attributes. This is now obsoleted in ES. Instead one has the "opportunity" to control almost every aspect of the rendering pipeline.