3d: Apply per-instance diffuse to mesh color

SetInstanceDiffuse has two roles depending on the instance type: for
directional lights it is the light color, and for meshes it is a
multiplier on the mesh color. xsystem4 honored only the former.

Treat inst->diffuse as color multiplier, via the diffuse_mod uniform.

include/reign.h

@@ -184,6 +184,7 @@ struct RE_instance {
 	bool use_mag_speed;
 	bool motion_blend;
 	float motion_blend_rate;
+	vec3 diffuse;  // color multiplier for meshes, light color for lights
 	vec3 ambient;
 	vec3 column_pos;
 	float column_height;
@@ -195,7 +196,6 @@ struct RE_instance {
 
 	// Lights
 	vec3 vec;
-	vec3 diffuse;
 	vec3 globe_diffuse;
 
 	// Private

src/3d/3d_internal.h

@@ -818,7 +818,7 @@ struct mpr_modulation {
 struct mpr *mpr_load(uint8_t *data, size_t size, struct model *model);
 void mpr_free(struct mpr *mpr);
 void mpr_evaluate_object(const struct mpr *mpr, float frame,
-		const struct RE_instance *inst, struct mpr_modulation *out);
+		struct RE_instance *inst, struct mpr_modulation *out);
 void mpr_evaluate_mesh(const struct mpr_track_set *mt, float frame,
 		const struct mpr_modulation *obj, struct mpr_modulation *out);
 void mpr_build_mat_tex_index(const struct model *model, const struct RE_instance *inst,

src/3d/mpr.c

@@ -244,11 +244,11 @@ static int eval_int(const struct mpr_int_key *keys, int nr, float frame, int fal
 
 // Combine inst defaults with .mpr Object-scope keyframes.
 void mpr_evaluate_object(const struct mpr *mpr, float frame,
-		const struct RE_instance *inst, struct mpr_modulation *out)
+		struct RE_instance *inst, struct mpr_modulation *out)
 {
 	out->alpha = inst->alpha;
-	glm_vec3_copy((float *)inst->ambient, out->ambient);
-	glm_vec3_one(out->diffuse);
+	glm_vec3_copy(inst->ambient, out->ambient);
+	glm_vec3_copy(inst->diffuse, out->diffuse);
 	if (!mpr)
 		return;
 	out->alpha *= eval_float(mpr->object.mul_alpha, mpr->object.nr_mul_alpha, frame, 1.f);

src/3d/reign.c

@@ -42,10 +42,9 @@ static struct RE_instance *create_instance(struct RE_plugin *plugin)
 	instance->plugin = plugin;
 	for (int i = 0; i < RE_NR_INSTANCE_TARGETS; i++)
 		instance->target[i] = -1;
-	instance->scale[0] = 1.0f;
-	instance->scale[1] = 1.0f;
-	instance->scale[2] = 1.0f;
+	glm_vec3_one(instance->scale);
 	instance->alpha = 1.0f;
+	glm_vec3_one(instance->diffuse);
 	instance->shadow_volume_bone_radius = 0.1f;
 	instance->draw_bump = true;
 	instance->fps = 30.0f;