//---------------------------------------------------------------------------------

//

//  File: GLSLHardwareSupport.c

//

//  Abstract: Check to see if fragment & vertex shader can execute in hardware.

//           

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//

//---------------------------------------------------------------------------------

//---------------------------------------------------------------------------------

#import "GLSLHardwareSupport.h"

//---------------------------------------------------------------------------------

#import <OpenGL/CGLRenderers.h>

//---------------------------------------------------------------------------------

//---------------------------------------------------------------------------------

static inline GLboolean CheckForExtension(const GLchar *extensionName, 

                                          const GLubyte *extensions)

{

    GLboolean  bExtensionAvailable = gluCheckExtension((GLubyte *)extensionName, 

                                                       extensions);

    return bExtensionAvailable;

} // CheckForExtension

//---------------------------------------------------------------------------------

static inline void CheckForAndLogExtensionAvailable(const GLboolean extensionAvailable, 

                                                    const GLchar *extensionName)

{

    if( extensionAvailable == GL_FALSE )

    {

        NSLog(@">> WARNING: \"%s\" extension is not available!\n", 

              extensionName);

    } // if

} // CheckForExtensions

//---------------------------------------------------------------------------------

static void CheckForShaders(NSOpenGLPixelFormatAttribute *thePixelAttributes)

{

    const GLubyte *extensions = glGetString(GL_EXTENSIONS);

    GLboolean  bShaderObjectAvailable      = CheckForExtension("GL_ARB_shader_objects", extensions);

    GLboolean  bShaderLanguage100Available = CheckForExtension("GL_ARB_shading_language_100", extensions);

    GLboolean  bVertexShaderAvailable      = CheckForExtension("GL_ARB_vertex_shader", extensions);

    GLboolean  bFragmentShaderAvailable    = CheckForExtension("GL_ARB_fragment_shader", extensions);

    GLboolean  bForceSoftwareRendering =    (bShaderObjectAvailable == GL_FALSE)

    ||  (bShaderLanguage100Available == GL_FALSE)

    ||  (bVertexShaderAvailable == GL_FALSE) 

    ||  (bFragmentShaderAvailable == GL_FALSE);

    if( bForceSoftwareRendering )

    {

        // Force software rendering, so fragment shaders will execute

        CheckForAndLogExtensionAvailable(bShaderObjectAvailable, "GL_ARB_shader_objects");

        CheckForAndLogExtensionAvailable(bShaderLanguage100Available, "GL_ARB_shading_language_100");

        CheckForAndLogExtensionAvailable(bVertexShaderAvailable, "GL_ARB_vertex_shader");

        CheckForAndLogExtensionAvailable(bFragmentShaderAvailable, "GL_ARB_fragment_shader");

        thePixelAttributes [3] = NSOpenGLPFARendererID;

        thePixelAttributes [4] = kCGLRendererGenericFloatID;

    } // if

} // CheckForShaders

//---------------------------------------------------------------------------------

static void CheckForClipVolumeHint(NSOpenGLPixelFormatAttribute *thePixelAttributes)

{

    const GLubyte *extensions = glGetString(GL_EXTENSIONS);

    // Inform OpenGL that the geometry is entirely within the 

    // view volume and that view-volume clipping is unnecessary. 

    // Normal clipping can be resumed by setting this hint to 

    // GL_DONT_CARE.  When clipping is disabled with this hint, 

    // results are undefined if geometry actually falls outside 

    //the view volume.

    GLboolean  bClipVolumeHintExtAvailable = CheckForExtension("GL_EXT_clip_volume_hint", 

                                                               extensions);

    if(   bClipVolumeHintExtAvailable == GL_TRUE)

    {

        glHint(GL_CLIP_VOLUME_CLIPPING_HINT_EXT,GL_FASTEST);

    } // if

} // CheckForClipVolumeHint

//---------------------------------------------------------------------------------

void CheckForGLSLHardwareSupport(NSOpenGLPixelFormatAttribute *thePixelAttributes)

{

    // Create a pre-flight context to check for GLSL hardware support

    NSOpenGLPixelFormat  *pixelFormat = [[NSOpenGLPixelFormat alloc] initWithAttributes:thePixelAttributes];

    if( pixelFormat != nil )

    {

        NSOpenGLContext *preflight = [[NSOpenGLContext alloc] initWithFormat:pixelFormat

                                                                shareContext:nil];

        if( preflight != nil )

        {

            [preflight makeCurrentContext];

            CheckForShaders(thePixelAttributes);

            CheckForClipVolumeHint(thePixelAttributes);

            [preflight   release];

        } // if

        [pixelFormat release];

    } // if

} // CheckForGLSLHardwareSupport

//---------------------------------------------------------------------------------

//---------------------------------------------------------------------------------