Add the EGL_MESA_configless_context extension

This extension provides a way for an application to render to multiple
surfaces with different buffer formats without having to use multiple
contexts. An EGLContext can be created without an EGLConfig by passing
EGL_NO_CONFIG_MESA. In that case there are no restrictions on the surfaces
that can be used with the context apart from that they must be using the same
EGLDisplay.

_mesa_initialze_context can now take a NULL gl_config which will mark the
context as ‘configless’. It will memset the visual to zero in that case.
Previously the i965 and i915 drivers were explicitly creating a zeroed visual
whenever 0 is passed for the EGLConfig. Mesa needs to be aware that the
context is configless because it affects the initial value to use for
glDrawBuffer. The first time the context is bound it will set the initial
value for configless contexts depending on whether the framebuffer used is
double-buffered.

Reviewed-by: Kristian Høgsberg <[email protected]>

1 files changed, 62 insertions, 20 deletions

diff --git a/src/mesa/main/context.c b/src/mesa/main/context.c
index 5b77ce103d2..cd009c11597 100644
--- a/src/mesa/main/context.c
+++ b/src/mesa/main/context.c
@@ -1013,7 +1013,8 @@ _mesa_initialize_dispatch_tables(struct gl_context *ctx)
  *
  * \param ctx the context to initialize
  * \param api the GL API type to create the context for
- * \param visual describes the visual attributes for this context
+ * \param visual describes the visual attributes for this context or NULL to
+ *               create a configless context
  * \param share_list points to context to share textures, display lists,
  *        etc with, or NULL
  * \param driverFunctions table of device driver functions for this context
@@ -1033,12 +1034,20 @@ _mesa_initialize_context(struct gl_context *ctx,
    assert(driverFunctions->FreeTextureImageBuffer);
 
    ctx->API = api;
-   ctx->Visual = *visual;
    ctx->DrawBuffer = NULL;
    ctx->ReadBuffer = NULL;
    ctx->WinSysDrawBuffer = NULL;
    ctx->WinSysReadBuffer = NULL;
 
+   if (visual) {
+      ctx->Visual = *visual;
+      ctx->HasConfig = GL_TRUE;
+   }
+   else {
+      memset(&ctx->Visual, 0, sizeof ctx->Visual);
+      ctx->HasConfig = GL_FALSE;
+   }
+
    if (_mesa_is_desktop_gl(ctx)) {
       _mesa_override_gl_version(ctx);
    }
@@ -1145,7 +1154,8 @@ fail:
  * the rendering context.
  *
  * \param api the GL API type to create the context for
- * \param visual a struct gl_config pointer (we copy the struct contents)
+ * \param visual a struct gl_config pointer (we copy the struct contents) or
+ *               NULL to create a configless context
  * \param share_list another context to share display lists with or NULL
  * \param driverFunctions points to the dd_function_table into which the
  *        driver has plugged in all its special functions.
@@ -1160,8 +1170,6 @@ _mesa_create_context(gl_api api,
 {
    struct gl_context *ctx;
 
-   ASSERT(visual);
-
    ctx = calloc(1, sizeof(struct gl_context));
    if (!ctx)
       return NULL;
@@ -1475,6 +1483,54 @@ _mesa_check_init_viewport(struct gl_context *ctx, GLuint width, GLuint height)
    }
 }
 
+static void
+handle_first_current(struct gl_context *ctx)
+{
+   GLenum buffer;
+   GLint bufferIndex;
+
+   assert(ctx->Version > 0);
+
+   ctx->Extensions.String = _mesa_make_extension_string(ctx);
+
+   check_context_limits(ctx);
+
+   /* According to GL_MESA_configless_context the default value of
+    * glDrawBuffers depends on the config of the first surface it is bound to.
+    * For GLES it is always GL_BACK which has a magic interpretation */
+   if (!ctx->HasConfig && _mesa_is_desktop_gl(ctx)) {
+      if (ctx->DrawBuffer != _mesa_get_incomplete_framebuffer()) {
+         if (ctx->DrawBuffer->Visual.doubleBufferMode)
+            buffer = GL_BACK;
+         else
+            buffer = GL_FRONT;
+
+         _mesa_drawbuffers(ctx, 1, &buffer, NULL /* destMask */);
+      }
+
+      if (ctx->ReadBuffer != _mesa_get_incomplete_framebuffer()) {
+         if (ctx->ReadBuffer->Visual.doubleBufferMode) {
+            buffer = GL_BACK;
+            bufferIndex = BUFFER_BACK_LEFT;
+         }
+         else {
+            buffer = GL_FRONT;
+            bufferIndex = BUFFER_FRONT_LEFT;
+         }
+
+         _mesa_readbuffer(ctx, buffer, bufferIndex);
+      }
+   }
+
+   /* We can use this to help debug user's problems.  Tell them to set
+    * the MESA_INFO env variable before running their app.  Then the
+    * first time each context is made current we'll print some useful
+    * information.
+    */
+   if (_mesa_getenv("MESA_INFO")) {
+      _mesa_print_info(ctx);
+   }
+}
 
 /**
  * Bind the given context to the given drawBuffer and readBuffer and
@@ -1567,21 +1623,7 @@ _mesa_make_current( struct gl_context *newCtx,
       }
 
       if (newCtx->FirstTimeCurrent) {
-         assert(newCtx->Version > 0);
-
-         newCtx->Extensions.String = _mesa_make_extension_string(newCtx);
-
-         check_context_limits(newCtx);
-
-         /* We can use this to help debug user's problems.  Tell them to set
-          * the MESA_INFO env variable before running their app.  Then the
-          * first time each context is made current we'll print some useful
-          * information.
-          */
-	 if (_mesa_getenv("MESA_INFO")) {
-	    _mesa_print_info(newCtx);
-	 }
-
+         handle_first_current(newCtx);
 	 newCtx->FirstTimeCurrent = GL_FALSE;
       }
    }