This script was tested and works on OpenSim version 0.7.4!

cannon_health.lsl
///////////////////////////////////////////////////////////////////////////
//  Copyright (C) Wizardry and Steamworks 2011 - License: GNU GPLv3      //
//  Please see: http://www.gnu.org/licenses/gpl.html for legal details,  //
//  rights of fair usage, the disclaimer and warranty conditions.        //
///////////////////////////////////////////////////////////////////////////
 
///////////////////////////////////////////////////////////////////////////
//                            CONFIGURATION                              //
///////////////////////////////////////////////////////////////////////////
 
// Set this to the total health. The maximum point-
// blank cannon shot will deal 30 damage which will be 
// deduced from the total health.
integer HEALTH = 100;
 
///////////////////////////////////////////////////////////////////////////
//                              INTERNALS                                //
///////////////////////////////////////////////////////////////////////////
 
///////////////////////////////////////////////////////////////////////////
//    Copyright (C) 2013 Wizardry and Steamworks - License: GNU GPLv3    //
///////////////////////////////////////////////////////////////////////////
 
string wasProgress(integer percent, integer length, list symbols) {
    percent /= (integer)((float)100.0/(length));
    string p = llList2String(symbols,0);
    integer itra = 0;
    do {
        if(itra>percent-1) p += llList2String(symbols,2);
        else p += llList2String(symbols,1);
    } while(++itra<length);
    return p + llList2String(symbols,3);
}
 
///////////////////////////////////////////////////////////////////////////
//    Copyright (C) 2013 Wizardry and Steamworks - License: GNU GPLv3    //
///////////////////////////////////////////////////////////////////////////
 
vector wasPercentToGradient(float percent, string rgb) {
    if(llStringLength(rgb) != 2) {
        llSay(DEBUG_CHANNEL, "Assert failed, rgb parameter must consist of a pair of either r, g, or b.");
        return ZERO_VECTOR;
    }
    string a = llGetSubString(rgb, 0, 0);
    string b = llGetSubString(rgb, 1, 1);
    list col = [ "r", "g", "b" ];
    integer ax = llListFindList(col, (list)a);
    integer bx = llListFindList(col, (list)b);
    if(ax == -1 || bx == -1) {
        llSay(DEBUG_CHANNEL, "Asset failed, rgb parameters must contain either r, g, or b letters.");
        return ZERO_VECTOR;
    }
    col = llListReplaceList(col, (list)((100-percent)/100), ax, ax);
    col = llListReplaceList(col, (list)(percent/100), bx, bx);
    return 2*<llList2Float(col, 0), llList2Float(col, 1), llList2Float(col, 2)>;
}
 
float h;
 
default
{
    state_entry() {
        h = HEALTH;
        llSetText("Health: " + wasProgress((integer)(h/HEALTH*100), 10, ["[", "█", "░", "]"]), wasPercentToGradient((integer)(h/HEALTH*100), "rg"), 1);
    }
    collision_start(integer num) {
        h -= llVecMag(llDetectedVel(0));
        llSetText("Health: " + wasProgress((integer)(h/HEALTH*100), 10, ["[", "█", "░", "]"]), wasPercentToGradient((integer)(h/HEALTH*100), "rg"), 1);
        if(h <= 0) state dead;
    }
}
 
state dead {
    state_entry() {
        llSetText("☠", <1,0,0>, 1);
        llSetTimerEvent(1);
    }
    timer() {
        llDie();
    }
}