Vanilla Code Questions

[DavidMedley]

I'm hacking around with vanilla at the moment. I'm going to post some questions as they come up.

My background: I don't have a lot of experience with C but I have 15+ years experience as a professional software developer. I'm more familiar with Perl than any other language.

[DavidMedley]

Where do things like PLAYER_LEVEL from class.txt get interpreted? I only find that string in text files and player-spell.c.

expression_base_value_f spell_value_base_by_name(const char *name)
{
	static const struct value_base_s {
		const char *name;
		expression_base_value_f function;
	} value_bases[] = {
		{ "SPELL_POWER", spell_value_base_spell_power },
		{ "PLAYER_LEVEL", spell_value_base_player_level },
		{ "DUNGEON_LEVEL", spell_value_base_dungeon_level },
		{ "MAX_SIGHT", spell_value_base_max_sight },
		{ "WEAPON_DAMAGE", spell_value_base_weapon_damage },
		{ "PLAYER_HP", spell_value_base_player_hp },
		{ "MONSTER_PERCENT_HP_GONE", spell_value_base_monster_percent_hp_gone },
		{ NULL, NULL },
	};
	const struct value_base_s *current = value_bases;

	while (current->name != NULL && current->function != NULL) {
		if (my_stricmp(name, current->name) == 0)
			return current->function;

		current++;
	}

	return NULL;
}

When I saw this I thought "Jackpot!" But when I try to put in things like WEAPON_DAMAGE into class.txt, angband gives me a parse error when I run it. I tried PLAYER_HP and DUNGEON_LEVEL as well and they give the same error, though MONSTER_PERCENT_HP_GONE obviously works since it's part of the Necro class.

So where are these codes, such as PLAYER_LEVEL and MONSTER_PERCENT_HP_GONE interpretted?

[DavidMedley]

Confirming: "s32b" means "signed 32 bit integer"? Example:

	s32b new_mana, new_mana_frac;

If so, why use this construction instead of "signed long int"? Or just "long" for brevity?

[wobbly]

Originally Posted by DavidMedley

Where do things like PLAYER_LEVEL from class.txt get interpreted? I only find that string in text files and player-spell.c.

expression_base_value_f spell_value_base_by_name(const char *name)
{
	static const struct value_base_s {
		const char *name;
		expression_base_value_f function;
	} value_bases[] = {
		{ "SPELL_POWER", spell_value_base_spell_power },
		{ "PLAYER_LEVEL", spell_value_base_player_level },
		{ "DUNGEON_LEVEL", spell_value_base_dungeon_level },
		{ "MAX_SIGHT", spell_value_base_max_sight },
		{ "WEAPON_DAMAGE", spell_value_base_weapon_damage },
		{ "PLAYER_HP", spell_value_base_player_hp },
		{ "MONSTER_PERCENT_HP_GONE", spell_value_base_monster_percent_hp_gone },
		{ NULL, NULL },
	};
	const struct value_base_s *current = value_bases;

	while (current->name != NULL && current->function != NULL) {
		if (my_stricmp(name, current->name) == 0)
			return current->function;

		current++;
	}

	return NULL;
}

When I saw this I thought "Jackpot!" But when I try to put in things like WEAPON_DAMAGE into class.txt, angband gives me a parse error when I run it. I tried PLAYER_HP and DUNGEON_LEVEL as well and they give the same error, though MONSTER_PERCENT_HP_GONE obviously works since it's part of the Necro class.

So where are these codes, such as PLAYER_LEVEL and MONSTER_PERCENT_HP_GONE interpretted?

look in init.c for Initialize player classes

[backwardsEric]

Originally Posted by DavidMedley

Confirming: "s32b" means "signed 32 bit integer"? Example:

	s32b new_mana, new_mana_frac;

If so, why use this construction instead of "signed long int"? Or just "long" for brevity?

Yes, it means a 32-bit signed integer. If one uses long, you don't have a guarantee about the size. For instance, when compiling 64-bit applications on Linux or Mac OS, a long is a 64-bit signed integer. There's a standard way of referring to integers with a known number of bits (int32_t, uint32_t, ....), and you'll see that used in h-basic.h to define what s32b is. But those types were introduced after Angband was originally written, and it's understandable that Angband adopted its own convention.

[wobbly]

Originally Posted by DavidMedley

When I saw this I thought "Jackpot!" But when I try to put in things like WEAPON_DAMAGE into class.txt, angband gives me a parse error when I run it. I tried PLAYER_HP and DUNGEON_LEVEL as well and they give the same error, though MONSTER_PERCENT_HP_GONE obviously works since it's part of the Necro class.

Changing:

spell:Magic Missile:1:1:22:4
effect:BOLT_OR_BEAM:MISSILE:0:-10
dice:$Dd4
expr:D:PLAYER_LEVEL:- 1 / 5 + 3
desc:Fires a magic missile that always hits its target and does
desc: unresistable damage.
desc:  Sometimes a beam is fired instead that hurts each monster
desc: in its path.
desc:  The chance to get a beam goes up with your character level.

to

spell:Magic Missile:1:1:22:4
effect:BOLT_OR_BEAM:MISSILE:0:-10
dice:$Dd4
expr:D:WEAPON_DAMAGE:- 1 / 5 + 3
desc:Fires a magic missile that always hits its target and does
desc: unresistable damage.
desc:  Sometimes a beam is fired instead that hurts each monster
desc: in its path.
desc:  The chance to get a beam goes up with your character level.

is working for me, & gives me a magic missile damage based on the dice of my weapon.

What parser error are you getting?

[DavidMedley]

Originally Posted by wobbly

is working for me

Hmm ok

expr:D:WEAPON_DAMAGE: #<--doesn't parse
expr:D:WEAPON_DAMAGE:+ 0 #<-- does parse

Thanks!

[DavidMedley]

Originally Posted by backwardsEric

those types were introduced after Angband was originally written

Makes sense. Thanks, Eric!

[DavidMedley]

Originally Posted by wobbly

look in init.c for Initialize player classes

OK. Now that we have the other thing figured out, hopefully I won't have to make any changes in here!

[DavidMedley]

OK, this is a pretty big ask, but I'll put it out into the universe and see what happens.

I want to create a spell that includes a melee blow as one of its effects. I've looked at

static bool py_attack_real(struct player *p, struct loc grid, bool *fear)
/**Attack the monster at the given location with a single blow.*/

And that seems to be perfect for what I have in mind, so I shouldn't have to write a whole new attack sequence.

But when I look at

bool spell_cast(int spell_index, int dir) {
...
	effect_do(spell->effect, source_player(), NULL, ident, true, dir, beam, 0)
...
}

It's really abstract and hard to follow. This probably makes it very flexible and powerful and (I'm hoping) pretty easy to get it to do what I want.

So can anyone provide me with hints or examples of how to do this?