Functions like glBlendEquation from GLExt are crashing (access violation) compiling on Mac with ppc386. The functions didn’t get loaded I think for some reason.

Is this is known problem on Mac with a work around perhaps?

Thanks.

Regards,
Ryan Joseph

Ryan Joseph wrote

Functions like glBlendEquation from GLExt are crashing (access violation) compiling on Mac with ppc386. The functions didn’t get loaded I think for some reason. Is this is known problem on Mac with a work around perhaps?

GLExt works fine on Mac (and other platforms) in my experience. You just have to load the necessary OpenGL version (or extension) first.

For glBlendEquation, you want to call Load_GL_version_1_2, and then (assuming Load_GL_version_1_2 returned true) glBlendEquation will be non-nil and will work OK.

Regards,
Michalis

Thanks I didn’t know any loading had to be called.

Does this work on OpenGLES 1.x do you know? I’m going to try this on iOS also.

Regards,
Ryan Joseph

Just tested on iOS and I get that error. I think on iOS it loads from the OpenGLES.framework and therefor this is failing. Also that load function wasn’t available but it failed upon including the GLExt unit.

An unhandled exception occurred at $00000001000CDEF7: Exception: Could not load OpenGL from /System/Library/Frameworks/OpenGL.framework/Libraries/libGL.dylib $00000001000CDEF7
$00000001000D0F85

On Jan 29, 2016, at 10:40 AM, Ryan Joseph wrote: Does this work on OpenGLES 1.x do you know? I’m going to try this on iOS also.

Regards,
Ryan Joseph

Um, GLExt is for OpenGL, it loads OpenGL extension, *not* for OpenGLES. For Android and iOS, use GLES20 unit. My Castle Game Engine uses this for Android and iOS and it works cool:)

Michalis

I’m using OpenGLES 1.1 because it was easier to learn but I don’t see glBlendEquation being included in the GLES11 unit. Maybe it didn’t exist until OpenGLES 2.0?

Regards,
Ryan Joseph

Ryan Joseph wrote

I’m using OpenGLES 1.1 because it was easier to learn but I don’t see glBlendEquation being included in the GLES11 unit. Maybe it didn’t exist until OpenGLES 2.0?

Indeed, glBlendEquation is simply not available in OpenGLES 1.1.

See the specs: https://www.khronos.org/opengles/ , e.g. the list of OpenGLES 1.1 functions on
https://www.khronos.org/opengles/sdk/1.1/docs/man/ .

Michalis

Is it available in any version before 2.0 do you know? I don’t know much about OpenGL but there is a 1.5 version also which maybe has it.

I found this page also which suggests it exists on some 1.x version.

http://stackoverflow.com/questions/17457327/blending-issue-porting-from-opengles-1-0-to-2-0-ios

On Jan 29, 2016, at 11:14 AM, Michalis Kamburelis wrote: Indeed, glBlendEquation is simply not available in OpenGLES 1.1.

Regards,
Ryan Joseph

Is it available in any version before 2.0 do you know?

No.

I don’t know much about OpenGL but there is a 1.5 version also which maybe has it.

Of course it has it but it is OpenGL 1.5 not OpenGL ES 1.5.

I found this page also which suggests it exists on some 1.x version. http://stackoverflow.com/questions/17457327/blending-issue-porting-from-opengles-1-0-to-2-0-ios

It's not in the specs so maybe Apple just added it for their implementation. You may want to take a look at the corresponding C header files provided by Apple.

Btw official specs and header files can be found here: https://www.khronos.org/

R.

P.S.: If your hardware allows move on to shader based OpenGL as the fixed function pipeline is inefficient on modern hardware and it teaches bad habits (like immediate mode usage or usage of glMatrix* calls).

Ryan Joseph wrote

Is it available in any version before 2.0 do you know? I don’t know much about OpenGL but there is a 1.5 version also which maybe has it.

Before OpenGLES version 2.0 (shader pipeline), you only have OpenGLES 1.1 and OpenGLES 1.0. See https://en.wikipedia.org/wiki/OpenGL_ES and https://www.khronos.org/opengles/1_X/ . Although OpenGLES 1.1 was based on (desktop) OpenGL 1.5, which included glBlendEquation (you can see it in https://www.opengl.org/documentation/specs/version1.5/glspec15.pdf ). But I guess glBlendEquation was not included in OpenGLES for simplicity --- OpenGLES was, by design, a very "trimmed down" version of (desktop) OpenGL.

And "glBlendEquation" is not available in OpenGLES 1.1. You have "glBlendFunc" in 1.1, but it only allows you to specify blending parameters, while blending equation is "hardcoded". Effectively, OpenGLES 1.1 always behaves like

glBlendEquation(GL_FUNC_ADD)

was called. You can see it e.g. by comparing glBlendFunc specifications for 1.1 and 2.0:
- https://www.khronos.org/opengles/sdk/1.1/docs/man/glBlendFunc.xml ,
- https://www.khronos.org/opengles/sdk/docs/man/xhtml/glBlendFunc.xml

In 1.1 version, the equation is simply hardcoded, while in 2.0 it can be configured by glBlendEquation.

Hmm, but there's this extension:
https://www.khronos.org/registry/gles/extensions/OES/OES_blend_subtract.txt . If this extension is supported, you could load glBlendEquationOES function, which should be what you need.

I'm not sure why the thread on
http://stackoverflow.com/questions/17457327/blending-issue-porting-from-opengles-1-0-to-2-0-ios suggests that glBlendEquation was used in OpenGLES 1.1. Maybe it's an Apple extension that, once you have OES_blend_subtract, you can load entry point "glBlendEquation", without "OES" suffix? Or maybe the poster on stackoverflow just simplified his/her code, to simplify the question?

Regards,
Michalis

Thanks for your response.

I’m seeing the method glBlendEquationOES in Apple’s headers so I assume this is available in the OpenGLES framework included with iOS (8.0 at least). Not sure how to load the extension though...

I’ll probably just deal with the default blending equation until I can implement 2.0. I was using glBlendEquation(GL_FUNC_ADD) anyways so that’s good to know I can just leave that line out and it will behave that anyways.

Regards,
Ryan Joseph