glGetString problem

[ptitSeb]

Hi,

I'm having some difficulties with a simple call in GL. I must do something wrong, but cannot get what.

When doing glGetString to have vendor or extensions string, most of the time I have just 0 as string (sign of error, but what error?).

Here is a simple test program "test.c":


#include <GLES2/gl2.h>
#include <stdio.h>
 
int main(int argc, char* argv[])
{
printf("Test of GLES2\n");
 
const char *sVendor = glGetString(GL_VENDOR);
printf("Vendor = %s\n", sVendor);
const char *sVersion = glGetString(GL_VERSION);
printf("Version = %s\n", sVersion);
}

and compile it with


gcc test.c -o test -lGLESv2

I always get (null) as string. Even when putting -lGLES_CM or adding -lEGL, same.

The only change is when using libGL of lunixboch, vendor is still (null), but I have a text for Version.

*EDIT*, I have checked, glGetError return NO_ERROR.

What is wrong?

 

[crow_riot]

i think a gl context must be initialized before. never had problems getting vendor strings

 

[ptitSeb]

i think a gl context must be initialized before. never had problems getting vendor strings

Yes, maybe, but I suspect that can be a problem in many software (GLEW included). Many tried to have the "Extensions" string before creating the display, so that can be problematic!

I'll try some simple "create context" / delete context in my simple test.

 

[ptitSeb]

Ok, I've create some context, and I've now some strings.

The sample program is now:

Spoiler

#include <GLES2/gl2.h>
#include <EGL/egl.h>
#include <stdio.h>
 
void print_gls(const char *str, const char *gls)
{
GLenum glerr;
if (gls) {
printf(str, gls);
} else {
glerr=glGetError();
printf("gl Error = ");
switch (glerr) {
case GL_NO_ERROR:
printf("NO_ERROR");
break;
case GL_INVALID_ENUM:
printf("GL_INVALID_ENUM");
break;
case GL_INVALID_VALUE:
printf("GL_INVALID_VALUE");
break;
case GL_INVALID_OPERATION:
printf("GL_INVALID_OPERATION");
break;
case GL_INVALID_FRAMEBUFFER_OPERATION:
printf("GL_INVALID_FRAMEBUFFER_OPERATION");
break;
case GL_OUT_OF_MEMORY:
printf("GL_OUT_OF_MEMORY");
break;
default:
printf("unknown");
}
printf("\n");
}
}
 
int main(int argc, char* argv[])
{
 printf("Test of GLES2\n");
 int maj, min;
 EGLDisplay d = eglGetDisplay(EGL_DEFAULT_DISPLAY);
 
 if (!eglInitialize(d, &maj, &min)) {
  printf("eglinfo: eglInitialize failed\n");
 }
 printf("EGL v%i.%i initialized\n", maj, min);
 EGLint attribs[] =
 {
  EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT,
  EGL_RED_SIZE, 1,
  EGL_GREEN_SIZE, 1,
  EGL_BLUE_SIZE, 1,
  EGL_NONE
 };
 EGLint ctx_attribs[] =
 {
 EGL_CONTEXT_CLIENT_VERSION, 2,
 EGL_NONE
 };
 
 
 EGLint num_configs;
 EGLConfig config;
 if (!eglChooseConfig(d, attribs, &config, 1, &num_configs) || (num_configs < 1))
 {
  printf("Could not find config for %s (perhaps this API is unsupported?)\n", "GLES2");
 }
 
 EGLint vid;
 if (!eglGetConfigAttrib(d, config, EGL_NATIVE_VISUAL_ID, &vid))
 {
  printf("Could not get native visual ID from chosen config\n");
 }
 eglBindAPI(EGL_OPENGL_ES_API);
 
 EGLContext ctx=eglCreateContext(d, config, EGL_NO_CONTEXT, ctx_attribs);
 EGLSurface srf=eglCreateWindowSurface(d, config, NULL, NULL);
 
 if (!eglMakeCurrent(d, srf, srf, ctx))
 { 
  printf("eglMakeCurrent() failed\n");
 }
 
 const char *sVendor = glGetString(GL_VENDOR);
 print_gls("Vendor = %s\n", sVendor);
 const char *sVersion = glGetString(GL_VERSION);
 print_gls("Version = %s\n", sVersion);
 const char *sRenderer = glGetString(GL_RENDERER);
 print_gls("Renderer = %s\n", sRenderer);
 const char *sExtensions = glGetString(GL_EXTENSIONS);
 print_gls("Extensions = %s\n", sExtensions); 
 
 eglDestroySurface(d, srf); 
 eglDestroyContext(d, ctx);
 eglTerminate(d);
}

And you compile it with 

gcc test.c -o test -lGLESv2 -lEGL

Now I have a nice output. So now, I may have a solution for Rice plugin, and all GLEW software that fail at init (because nobody expect a simple glGetString to return null! )

 

[ptitSeb]

Hum, maybe I also miss a little


eglMakeCurrent(d, EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT);


before the eglDestroy...

 

[mcobit]

Hum... so this was the problem with TileMassacreSHMUP, too?


Good that you found a solution


Awaiting pnd ...

 

[ptitSeb]

Hum... so this was the problem with TileMassacreSHMUP, too?


Good that you found a solution


Awaiting pnd ...

Not sure, I think I have another problem with this one. Just adding a "SDL_Init" 1st line in main make it hang, so I have something wrong with the linker or something like that. I'm play with muppen for now (because gthumb p**s me off, the slideshow works, but hang at the exit, veeeery anoying).

 

[Pickle]

ive only seen null when the egl context has failed or didnt work. you will get different output for 1.X ES vs 2.0