mesa: Define infrastructure for ARB_framebuffer_no_attachments

Define the infrastructure for the extension GL_ARB_framebuffer_no_attachments:
 - extension table
 - additions to gl_framebuffer

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Signed-off-by: Kevin Rogovin <kevin.rogovin@intel.com>

src/mesa/main/extensions.c

@@ -117,6 +117,7 @@ static const struct extension extension_table[] = {
    { "GL_ARB_fragment_program",                    o(ARB_fragment_program),                    GLL,            2002 },
    { "GL_ARB_fragment_program_shadow",             o(ARB_fragment_program_shadow),             GLL,            2003 },
    { "GL_ARB_fragment_shader",                     o(ARB_fragment_shader),                     GL,             2002 },
+   { "GL_ARB_framebuffer_no_attachments",          o(ARB_framebuffer_no_attachments),          GL,             2012 },
    { "GL_ARB_framebuffer_object",                  o(ARB_framebuffer_object),                  GL,             2005 },
    { "GL_ARB_framebuffer_sRGB",                    o(EXT_framebuffer_sRGB),                    GL,             1998 },
    { "GL_ARB_get_program_binary",                  o(dummy_true),                              GL,             2010 },

src/mesa/main/fbobject.c

@@ -957,6 +957,7 @@ _mesa_test_framebuffer_completeness(struct gl_context *ctx,
    fb->Height = 0;
    fb->_AllColorBuffersFixedPoint = GL_TRUE;
    fb->_HasSNormOrFloatColorBuffer = GL_FALSE;
+   fb->_HasAttachments = true;
 
    /* Start at -2 to more easily loop over all attachment points.
     *  -2: depth buffer

src/mesa/main/framebuffer.c

@@ -157,6 +157,7 @@ _mesa_initialize_window_framebuffer(struct gl_framebuffer *fb,
    fb->_Status = GL_FRAMEBUFFER_COMPLETE_EXT;
    fb->_AllColorBuffersFixedPoint = !visual->floatMode;
    fb->_HasSNormOrFloatColorBuffer = visual->floatMode;
+   fb->_HasAttachments = true;
 
    compute_depth_max(fb);
 }

src/mesa/main/mtypes.h

@@ -3133,12 +3133,29 @@ struct gl_framebuffer
     */
    struct gl_config Visual;
 
-   GLuint Width, Height;	/**< size of frame buffer in pixels */
+   /**
+    * Size of frame buffer in pixels. If there are no attachments, then both
+    * of these are 0.
+    */
+   GLuint Width, Height;
 
-   /** \name  Drawing bounds (Intersection of buffer size and scissor box) */
+   /**
+    * In the case that the framebuffer has no attachment (i.e.
+    * GL_ARB_framebuffer_no_attachments) then the geometry of
+    * the framebuffer is specified by the default values.
+    */
+   struct {
+     GLuint Width, Height, Layers, NumSamples;
+     GLboolean FixedSampleLocations;
+   } DefaultGeometry;
+
+   /** \name  Drawing bounds (Intersection of buffer size and scissor box)
+    * The drawing region is given by [_Xmin, _Xmax) x [_Ymin, _Ymax),
+    * (inclusive for _Xmin and _Ymin while exclusive for _Xmax and _Ymax)
+    */
    /*@{*/
-   GLint _Xmin, _Xmax;  /**< inclusive */
-   GLint _Ymin, _Ymax;  /**< exclusive */
+   GLint _Xmin, _Xmax;
+   GLint _Ymin, _Ymax;
    /*@}*/
 
    /** \name  Derived Z buffer stuff */
@@ -3151,6 +3168,16 @@ struct gl_framebuffer
    /** One of the GL_FRAMEBUFFER_(IN)COMPLETE_* tokens */
    GLenum _Status;
 
+   /** Whether one of Attachment has Type != GL_NONE
+    * NOTE: the values for Width and Height are set to 0 in case of having
+    * no attachments, a backend driver supporting the extension
+    * GL_ARB_framebuffer_no_attachments must check for the flag _HasAttachments
+    * and if GL_FALSE, must then use the values in DefaultGeometry to initialize
+    * its viewport, scissor and so on (in particular _Xmin, _Xmax, _Ymin and
+    * _Ymax do NOT take into account _HasAttachments being false)
+    */
+   bool _HasAttachments;
+
    /** Integer color values */
    GLboolean _IntegerColor;
 
@@ -3161,7 +3188,9 @@ struct gl_framebuffer
    /**
     * The maximum number of layers in the framebuffer, or 0 if the framebuffer
     * is not layered.  For cube maps and cube map arrays, each cube face
-    * counts as a layer.
+    * counts as a layer. As the case for Width, Height a backend driver
+    * supporting GL_ARB_framebuffer_no_attachments must use DefaultGeometry
+    * in the case that _HasAttachments is false
     */
    GLuint MaxNumLayers;
 
@@ -3340,6 +3369,14 @@ struct gl_constants
    GLuint MaxRenderbufferSize;   /**< GL_EXT_framebuffer_object */
    GLuint MaxSamples;            /**< GL_ARB_framebuffer_object */
 
+   /**
+    * GL_ARB_framebuffer_no_attachments
+    */
+   GLuint MaxFramebufferWidth;
+   GLuint MaxFramebufferHeight;
+   GLuint MaxFramebufferLayers;
+   GLuint MaxFramebufferSamples;
+
    /** Number of varying vectors between any two shader stages. */
    GLuint MaxVarying;
 
@@ -3617,6 +3654,7 @@ struct gl_extensions
    GLboolean ARB_fragment_program;
    GLboolean ARB_fragment_program_shadow;
    GLboolean ARB_fragment_shader;
+   GLboolean ARB_framebuffer_no_attachments;
    GLboolean ARB_framebuffer_object;
    GLboolean ARB_explicit_attrib_location;
    GLboolean ARB_explicit_uniform_location;