SC2Mapster

How would I go about using this "catalog function"?

Use them in the way I described above.

Here is an example trigger that when pressing esc it will print out all base damage amounts of all weapons (including hidden) for all selected units.

Weapon Damage Test
    Events
        UI - Player Any Player presses Escape key Down with shift Allow, control Allow, alt Allow
    Local Variables
        display player = (Triggering player) <Integer>
        display player group = (Player group(display player)) <Player Group>
        u = No Unit <Unit>
        p = 0 <Integer>
        i = 0 <Integer>
        weapon n = 0 <Integer>
        weapon = No Game Link <Game Link - Weapon>
        effect = No Game Link <Game Link - Effect>
        damage = 0.0 <Real>
        text = No Text <Text>
    Conditions
    Actions
        Unit Group - For each unit u in (Selected units for player (Triggering player)) do (Actions)
            Actions
                Variable - Set p = (Owner of u)
                Variable - Set i = 1
                Variable - Set weapon n = (Number of weapons on u)
                General - While (Conditions) are true, do (Actions)
                    Conditions
                        i <= weapon n
                    Actions
                        Variable - Set weapon = (u weapon i)
                        Variable - Set effect = (Game Link((Value of Weapons weapon DisplayEffect for player p)))
                        Variable - Set damage = (Real((Value of Effects effect Amount for player p)))
                        Variable - Set text = (Combine ((Text((Unit tag of u))), " ", (Name of u), " : ", (Game text for (Value of Weapons weapon Name for player p)), " -> ", (Text(damage) with Any Precision decimal places)))
                        UI - Display text for display player group to Subtitle area
                        Variable - Modify i: + 1

 Here is the same trigger but in galaxy form.

//--------------------------------------------------------------------------------------------------
// Trigger: Weapon Damage Test
//--------------------------------------------------------------------------------------------------
bool gt_WeaponDamageTest_Func (bool testConds, bool runActions) {
    unitgroup autoE0F39D3A_g;
    int autoE0F39D3A_u;

    // Variable Declarations
    int lv_displayplayer;
    playergroup lv_displayplayergroup;
    unit lv_u;
    int lv_p;
    int lv_i;
    int lv_weaponn;
    string lv_weapon;
    string lv_effect;
    fixed lv_damage;
    text lv_text;

    // Variable Initialization
    lv_displayplayer = EventPlayer();
    lv_displayplayergroup = PlayerGroupSingle(lv_displayplayer);

    // Actions
    if (!runActions) {
        return true;
    }

    autoE0F39D3A_g = UnitGroupSelected(EventPlayer());
    autoE0F39D3A_u = 1;
    for ( ; autoE0F39D3A_u <= UnitGroupCount(autoE0F39D3A_g, c_unitCountAll) ; autoE0F39D3A_u += BoolToInt(lv_u == UnitGroupUnit(autoE0F39D3A_g, autoE0F39D3A_u)) ) {
        lv_u = UnitGroupUnit(autoE0F39D3A_g, autoE0F39D3A_u);
        lv_p = UnitGetOwner(lv_u);
        lv_i = 1;
        lv_weaponn = UnitWeaponCount(lv_u);
        while ((lv_i <= lv_weaponn)) {
            lv_weapon = UnitWeaponGet(lv_u, lv_i);
            lv_effect = (CatalogFieldValueGet(c_gameCatalogWeapon, lv_weapon, "DisplayEffect", lv_p));
            lv_damage = StringToFixed(CatalogFieldValueGet(c_gameCatalogEffect, lv_effect, "Amount", lv_p));
            lv_text = (IntToText(UnitGetTag(lv_u)) + StringExternal("Param/Value/20394F82") + UnitGetName(lv_u) + StringExternal("Param/Value/909747C7") + StringExternal(CatalogFieldValueGet(c_gameCatalogWeapon, lv_weapon, "Name", lv_p)) + StringExternal("Param/Value/40D4849B") + FixedToText(lv_damage, c_fixedPrecisionAny));
            UIDisplayMessage(lv_displayplayergroup, c_messageAreaSubtitle, lv_text);
            lv_i += 1;
        }
    }
    return true;
}

//--------------------------------------------------------------------------------------------------
void gt_WeaponDamageTest_Init () {
    gt_WeaponDamageTest = TriggerCreate("gt_WeaponDamageTest_Func");
    TriggerAddEventKeyPressed(gt_WeaponDamageTest, c_playerAny, c_keyEscape, true, c_keyModifierStateIgnore, c_keyModifierStateIgnore, c_keyModifierStateIgnore);
}

How would I use triggers to find the damage of the caster's current weapon?

You can dynamically lookup the weapon a unit is using, then use catalog functions to look up its tooltip damage effect (which should be the weapon damage) and then use catalog functions again to get the damage effect's various damage fields. You then multiply this by your damage factor, and use triggers to deal the damage to the appropriate unit. Trigger dealt damage will automatically inherit all damage modifiers from the source (damaging) unit as permitted by the effect used to deal the damage. Eg if a unit has +400% weapon damage and the damage effect used is modified by weapon damage then the trigger damage will also deal +400%, hence why it is sufficient to look up the base effect damage.

For usability I recommend a trigger enhanced effect to do this. A trigger enhanced effect is a dummy effect, eg a Set effect that does nothing, that is used to fire a trigger using the Effect trigger event. As the event references a single effect link, the trigger will only fire when that dummy effect is used making it very efficient and highly scalable. Since a dummy effect is used, it merges seamlessly with data and the effect can be used in place of a normal damage effect. The trigger would resolve the weapon damage of the effect source unit, compute the damage to deal, and then deal damage from source effect unit to target effect unit using an appropriate Damage effect, which could be either a generic dummy damage effect used by many triggers or a special purpose dummy effect created just for a specific source of damage.