Add explicit error messages to Multimesh error functions to make errors easier to understand.

Previously the RenderingServer errors filtered up to end users, but they are unclear and not helpful

scene/resources/multimesh.cpp

@@ -198,6 +198,12 @@ void MultiMesh::set_buffer(const Vector<float> &p_buffer) {
 	if (instance_count == 0) {
 		return;
 	}
+
+	uint32_t stride = transform_format == TRANSFORM_2D ? 8 : 12;
+	stride += use_colors ? 4 : 0;
+	stride += use_custom_data ? 4 : 0;
+	ERR_FAIL_COND_MSG(stride * instance_count != p_buffer.size(), "Cannot set a buffer on a Multimesh that is a different size from the Multimesh's existing buffer.");
+
 	RS::get_singleton()->multimesh_set_buffer(multimesh, p_buffer);
 }
 
@@ -249,39 +255,56 @@ void MultiMesh::set_physics_interpolation_quality(PhysicsInterpolationQuality p_
 }
 
 void MultiMesh::set_instance_transform(int p_instance, const Transform3D &p_transform) {
+	ERR_FAIL_INDEX_MSG(p_instance, instance_count, "Instance index out of bounds. Instance index must be less than `instance_count` and greater than or equal to zero.");
+	ERR_FAIL_COND_MSG(transform_format == TRANSFORM_2D, "Can't set Transform3D on a Multimesh configured to use Transform2D. Ensure that you have set the `transform_format` to `TRANSFORM_3D`.");
 	RenderingServer::get_singleton()->multimesh_instance_set_transform(multimesh, p_instance, p_transform);
 }
 
 void MultiMesh::set_instance_transform_2d(int p_instance, const Transform2D &p_transform) {
+	ERR_FAIL_INDEX_MSG(p_instance, instance_count, "Instance index out of bounds. Instance index must be less than `instance_count` and greater than or equal to zero.");
+	ERR_FAIL_COND_MSG(transform_format == TRANSFORM_3D, "Can't set Transform2D on a Multimesh configured to use Transform3D. Ensure that you have set the `transform_format` to `TRANSFORM_2D`.");
 	RenderingServer::get_singleton()->multimesh_instance_set_transform_2d(multimesh, p_instance, p_transform);
 	emit_changed();
 }
 
 Transform3D MultiMesh::get_instance_transform(int p_instance) const {
+	ERR_FAIL_INDEX_V_MSG(p_instance, instance_count, Transform3D(), "Instance index out of bounds. Instance index must be less than `instance_count` and greater than or equal to zero.");
+	ERR_FAIL_COND_V_MSG(transform_format == TRANSFORM_2D, Transform3D(), "Can't get Transform3D on a Multimesh configured to use Transform2D. Ensure that you have set the `transform_format` to `TRANSFORM_3D`.");
 	return RenderingServer::get_singleton()->multimesh_instance_get_transform(multimesh, p_instance);
 }
 
 Transform2D MultiMesh::get_instance_transform_2d(int p_instance) const {
+	ERR_FAIL_INDEX_V_MSG(p_instance, instance_count, Transform2D(), "Instance index out of bounds. Instance index must be less than `instance_count` and greater than or equal to zero.");
+	ERR_FAIL_COND_V_MSG(transform_format == TRANSFORM_3D, Transform2D(), "Can't get Transform2D on a Multimesh configured to use Transform3D. Ensure that you have set the `transform_format` to `TRANSFORM_2D`.");
 	return RenderingServer::get_singleton()->multimesh_instance_get_transform_2d(multimesh, p_instance);
 }
 
 void MultiMesh::set_instance_color(int p_instance, const Color &p_color) {
+	ERR_FAIL_INDEX_MSG(p_instance, instance_count, "Instance index out of bounds. Instance index must be less than `instance_count` and greater than or equal to zero.");
+	ERR_FAIL_COND_MSG(!use_colors, "Can't set instance color on a Multimesh that isn't using colors. Ensure that you have `use_colors` property of this Multimesh set to `true`.");
 	RenderingServer::get_singleton()->multimesh_instance_set_color(multimesh, p_instance, p_color);
 }
 
 Color MultiMesh::get_instance_color(int p_instance) const {
+	ERR_FAIL_INDEX_V_MSG(p_instance, instance_count, Color(), "Instance index out of bounds. Instance index must be less than `instance_count` and greater than or equal to zero.");
+	ERR_FAIL_COND_V_MSG(!use_colors, Color(), "Can't get instance color on a Multimesh that isn't using colors. Ensure that you have `use_colors` property of this Multimesh set to `true`.");
 	return RenderingServer::get_singleton()->multimesh_instance_get_color(multimesh, p_instance);
 }
 
 void MultiMesh::set_instance_custom_data(int p_instance, const Color &p_custom_data) {
+	ERR_FAIL_INDEX_MSG(p_instance, instance_count, "Instance index out of bounds. Instance index must be less than `instance_count` and greater than or equal to zero.");
+	ERR_FAIL_COND_MSG(!use_custom_data, "Can't get instance custom data on a Multimesh that isn't using custom data. Ensure that you have `use_custom_data` property of this Multimesh set to `true`.");
 	RenderingServer::get_singleton()->multimesh_instance_set_custom_data(multimesh, p_instance, p_custom_data);
 }
 
 Color MultiMesh::get_instance_custom_data(int p_instance) const {
+	ERR_FAIL_INDEX_V_MSG(p_instance, instance_count, Color(), "Instance index out of bounds. Instance index must be less than `instance_count` and greater than or equal to zero.");
+	ERR_FAIL_COND_V_MSG(!use_custom_data, Color(), "Can't get instance custom data on a Multimesh that isn't using custom data. Ensure that you have `use_custom_data` property of this Multimesh set to `true`.");
 	return RenderingServer::get_singleton()->multimesh_instance_get_custom_data(multimesh, p_instance);
 }
 
 void MultiMesh::reset_instance_physics_interpolation(int p_instance) {
+	ERR_FAIL_INDEX_MSG(p_instance, instance_count, "Instance index out of bounds. Instance index must be less than `instance_count` and greater than or equal to zero.");
 	RenderingServer::get_singleton()->multimesh_instance_reset_physics_interpolation(multimesh, p_instance);
 }
 
@@ -308,7 +331,7 @@ RID MultiMesh::get_rid() const {
 }
 
 void MultiMesh::set_use_colors(bool p_enable) {
-	ERR_FAIL_COND(instance_count > 0);
+	ERR_FAIL_COND_MSG(instance_count > 0, "Instance count must be 0 to toggle whether colors are used.");
 	use_colors = p_enable;
 }
 
@@ -317,7 +340,7 @@ bool MultiMesh::is_using_colors() const {
 }
 
 void MultiMesh::set_use_custom_data(bool p_enable) {
-	ERR_FAIL_COND(instance_count > 0);
+	ERR_FAIL_COND_MSG(instance_count > 0, "Instance count must be 0 to toggle whether custom data is used.");
 	use_custom_data = p_enable;
 }
 
@@ -326,7 +349,7 @@ bool MultiMesh::is_using_custom_data() const {
 }
 
 void MultiMesh::set_transform_format(TransformFormat p_transform_format) {
-	ERR_FAIL_COND(instance_count > 0);
+	ERR_FAIL_COND_MSG(instance_count > 0, "Instance count must be 0 to change the transform format.");
 	transform_format = p_transform_format;
 }