cogl-gles2-context: Cast func pointers to void* when filling

vtable

(Sorry, I had to re-apply Neil's patch as the original one somehow did
 not apply)

The function prototypes for the GL functions in CoglContext have the
GLAPIENTRY attribute which on Windows makes them use the stdcall
calling convention. The function pointers exposed from cogl-gles2.h
don't have GLAPIENTRY so they end up having a different calling
convention on Windows. When Cogl is compiled there it ends up giving a
lot of warnings because it assigns a pointer to an incompatible
function type.

We probably don't want to make the functions exposed in cogl-gles2.h
use the stdcall calling convention because we control that API so
there is no need to introduce a second calling convention. The GLES2
context support currently isn't going to work on Windows anyway
because there is no EGL or GLES2 implementation.

Eventually if we make the Cogl GLES2 context virtualized on top of
Cogl then we will provide our own implementations of all these
functions so we can easily keep the C calling convention even on
Windows.

Until then to avoid the warnings on Windows we can just cast the
function pointers temporarily to (void*) when filling in the vtable.

This will also fix the build on Windows using Visual Studio, as it is
more picky on calling convention mismatches.

Reviewed-by: Robert Bragg <robert@linux.intel.com>

1 files changed, 10 insertions, 5 deletions

diff --git a/cogl/cogl-gles2-context.c b/cogl/cogl-gles2-context.c
index 2e727861..ed95b696 100644
--- a/cogl/cogl-gles2-context.c
+++ b/cogl/cogl-gles2-context.c
@@ -1597,7 +1597,7 @@ cogl_gles2_context_new (CoglContext *ctx, GError **error)
                        extension_suffixes, extension_names)
 
 #define COGL_EXT_FUNCTION(ret, name, args) \
-  gles2_ctx->vtable->name = ctx->name;
+  gles2_ctx->vtable->name = (void *) ctx->name;
 
 #define COGL_EXT_END()
 
@@ -1607,10 +1607,15 @@ cogl_gles2_context_new (CoglContext *ctx, GError **error)
 #undef COGL_EXT_FUNCTION
 #undef COGL_EXT_END
 
-  gles2_ctx->vtable->glBindFramebuffer = gl_bind_framebuffer_wrapper;
-  gles2_ctx->vtable->glReadPixels = gl_read_pixels_wrapper;
-  gles2_ctx->vtable->glCopyTexImage2D = gl_copy_tex_image_2d_wrapper;
-  gles2_ctx->vtable->glCopyTexSubImage2D = gl_copy_tex_sub_image_2d_wrapper;
+  gles2_ctx->vtable->glBindFramebuffer =
+    (void *) gl_bind_framebuffer_wrapper;
+  gles2_ctx->vtable->glReadPixels =
+    (void *) gl_read_pixels_wrapper;
+  gles2_ctx->vtable->glCopyTexImage2D =
+    (void *) gl_copy_tex_image_2d_wrapper;
+  gles2_ctx->vtable->glCopyTexSubImage2D =
+    (void *) gl_copy_tex_sub_image_2d_wrapper;
+
   gles2_ctx->vtable->glCreateShader = gl_create_shader_wrapper;
   gles2_ctx->vtable->glDeleteShader = gl_delete_shader_wrapper;
   gles2_ctx->vtable->glCreateProgram = gl_create_program_wrapper;