gl-renderer: add support for (a|x)bgr16161616f shm formats

These formats will be eventually be useful for color managed clients
using wl_shm that wish to submit buffers encoding high dynamic range
images.

While the minimum requirement for linearly filterable half float
textures is GL ES 2.0 + GL_OES_texture_half_float_linear, to keep
the code simple, this commit only enables the new formats when
the requirements for color management (notably including GL ES 3.0
and GL_EXT_color_buffer_half_float) are available.

Signed-off-by: Manuel Stoeckl <code@mstoeckl.com>

libweston/renderer-gl/gl-renderer.c

@@ -1821,6 +1821,7 @@ gl_format_from_internal(GLenum internal_format)
 		return GL_RED_EXT;
 	case GL_RG8_EXT:
 		return GL_RG_EXT;
+	case GL_RGBA16F:
 	case GL_RGB10_A2:
 		return GL_RGBA;
 	default:
@@ -2015,6 +2016,24 @@ gl_renderer_attach_shm(struct weston_surface *es, struct weston_buffer *buffer,
 		gl_pixel_type = GL_UNSIGNED_INT_2_10_10_10_REV_EXT;
 		es->is_opaque = true;
 		break;
+	case WL_SHM_FORMAT_ABGR16161616F:
+		if (!gr->gl_supports_color_transforms)
+			goto unsupported;
+		gs->shader_variant = SHADER_VARIANT_RGBA;
+		pitch = wl_shm_buffer_get_stride(shm_buffer) / 8;
+		gl_format[0] = GL_RGBA16F;
+		gl_pixel_type = GL_HALF_FLOAT;
+		es->is_opaque = false;
+		break;
+	case WL_SHM_FORMAT_XBGR16161616F:
+		if (!gr->gl_supports_color_transforms)
+			goto unsupported;
+		gs->shader_variant = SHADER_VARIANT_RGBX;
+		pitch = wl_shm_buffer_get_stride(shm_buffer) / 8;
+		gl_format[0] = GL_RGBA16F;
+		gl_pixel_type = GL_HALF_FLOAT;
+		es->is_opaque = true;
+		break;
 #endif
 	case WL_SHM_FORMAT_YUV420:
 		gs->shader_variant = SHADER_VARIANT_Y_U_V;
@@ -3699,6 +3718,10 @@ gl_renderer_display_create(struct weston_compositor *ec,
 		wl_display_add_shm_format(ec->wl_display, WL_SHM_FORMAT_ABGR2101010);
 		wl_display_add_shm_format(ec->wl_display, WL_SHM_FORMAT_XBGR2101010);
 	}
+	if (gr->gl_supports_color_transforms) {
+		wl_display_add_shm_format(ec->wl_display, WL_SHM_FORMAT_ABGR16161616F);
+		wl_display_add_shm_format(ec->wl_display, WL_SHM_FORMAT_XBGR16161616F);
+	}
 #endif
 
 	if (gr->gl_supports_color_transforms)