fix headless import attempting to load graphics driver

Author: TCROC

modules/betsy/image_compress_betsy.cpp

@@ -36,11 +36,16 @@
 
 #include "bc1.glsl.gen.h"
 #include "bc6h.glsl.gen.h"
+#include "servers/display_server.h"
 
 static Mutex betsy_mutex;
 static BetsyCompressor *betsy = nullptr;
 
 void BetsyCompressor::_init() {
+	if (!DisplayServer::can_create_rendering_device()) {
+		return;
+	}
+
 	// Create local RD.
 	RenderingContextDriver *rcd = nullptr;
 	RenderingDevice *rd = RenderingServer::get_singleton()->create_local_rendering_device();
@@ -177,6 +182,11 @@ static String get_shader_name(BetsyFormat p_format) {
 Error BetsyCompressor::_compress(BetsyFormat p_format, Image *r_img) {
 	uint64_t start_time = OS::get_singleton()->get_ticks_msec();
 
+	// Return an error so that the compression can fall back to cpu compression
+	if (compress_rd == nullptr) {
+		return ERR_CANT_CREATE;
+	}
+
 	if (r_img->is_compressed()) {
 		return ERR_INVALID_DATA;
 	}

servers/display_server.cpp

@@ -1229,6 +1229,10 @@ void DisplayServer::_input_set_custom_mouse_cursor_func(const Ref<Resource> &p_i
 }
 
 bool DisplayServer::can_create_rendering_device() {
+	if (get_singleton()->get_name() == "headless") {
+		return false;
+	}
+
 #if defined(RD_ENABLED)
 	RenderingDevice *device = RenderingDevice::get_singleton();
 	if (device) {

servers/rendering/rendering_device_binds.cpp

@@ -31,7 +31,10 @@
 #include "rendering_device_binds.h"
 
 Error RDShaderFile::parse_versions_from_text(const String &p_text, const String p_defines, OpenIncludeFunction p_include_func, void *p_include_func_userdata) {
-	ERR_FAIL_NULL_V(RenderingDevice::get_singleton(), ERR_UNAVAILABLE);
+	ERR_FAIL_NULL_V_MSG(
+			RenderingDevice::get_singleton(),
+			ERR_UNAVAILABLE,
+			"Cannot import custom .glsl shaders when running without a RenderingDevice. This can happen if you are using the headless more or the Compatibility backend.");
 
 	Vector<String> lines = p_text.split("\n");