var DT_TOP = 0x00000000;
var DT_CENTER = 0x00000001;
var DT_VCENTER = 0x00000004;
var DT_WORDBREAK = 0x00000010;
var DT_CALCRECT = 0x00000400;
var DT_NOPREFIX = 0x00000800;

String.prototype.repeat = function( num ) {
    return new Array( num + 1 ).join( this );
}

var g_font = gdi.Font("Tahoma", 12);
var g_text = ("Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.\n" +
    "Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.\n" +
    "Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur.\n" + 
    "Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.\n\n").repeat(5);

var ww = 0, wh = 0;
var g_textcolor = 0xff000000;
var g_backcolor = 0xffffffff;
var g_need_calc = true;
var g_textheight = 0;
var g_offset = 0;
var g_drag = false;
var g_drag_y = 0;

// START
function on_size() {
    ww = window.Width;
    wh = window.Height;
    reset();
}

function on_paint(gr) {
    gr.FillSolidRect(0, 0, ww, wh, g_backcolor);
    
    if (g_need_calc) {
        calc();
    } else {
        gr.GdiDrawText(g_text, g_font, g_textcolor, 0, g_offset, ww, wh - g_offset, DT_CENTER | DT_WORDBREAK | DT_NOPREFIX);
    }
}

function on_mouse_lbtn_down(x, y) {
    g_drag = true;
    g_drag_y = y;
}

function on_mouse_lbtn_up(x, y) {
    g_drag = false;
}

function on_mouse_move(x, y) {
    if (g_drag) {
        applyDelta(y - g_drag_y);
        g_drag_y = y;
    }
}

function on_mouse_wheel(step) {
    applyDelta(step * 20);
}

function calc() {
    // Using a temp IGdiGraphics interface
    var temp_bmp = gdi.CreateImage(1, 1);
    var temp_gr = temp_bmp.GetGraphics();
    
    // Calculate
    arr = temp_gr.GdiDrawText(g_text, g_font, g_textcolor, 0, 0, ww, wh, DT_VCENTER | DT_CENTER | DT_WORDBREAK | DT_CALCRECT | DT_NOPREFIX).toArray();
    g_textheight = arr[3] - arr[1];
    g_offset = wh / 2;
    g_need_calc = false;
    
    // Free the resources
    temp_bmp.ReleaseGraphics(temp_gr);
    temp_bmp.Dispose();
    temp_gr = null;
    temp_bmp = null;
    window.Repaint();
}

function applyDelta(delta) {
    var temp = g_offset + delta;
    
    if ((temp <= wh / 2) && (temp >= wh / 2 - g_textheight)) {
        g_offset = temp;
        window.Repaint();
    }
}

function reset() {
    g_need_calc = true;
    g_offset = 0;
}