SquirrelJME/SquirrelJME

// -*- Mode: Java; indent-tabs-mode: t; tab-width: 4 -*-
// ---------------------------------------------------------------------------
// SquirrelJME
//     Copyright (C) Stephanie Gawroriski <xer@multiphasicapps.net>
// ---------------------------------------------------------------------------
// SquirrelJME is under the Mozilla Public License Version 2.0.
// See license.mkd for licensing and copyright information.
// ---------------------------------------------------------------------------

package cc.squirreljme.runtime.lcdui.mle;

import cc.squirreljme.jvm.mle.UIFormShelf;
import cc.squirreljme.jvm.mle.brackets.UIDisplayBracket;
import cc.squirreljme.jvm.mle.constants.UIMetricType;
import cc.squirreljme.jvm.mle.constants.UIPixelFormat;
import cc.squirreljme.runtime.cldc.annotation.SquirrelJMEVendorApi;
import cc.squirreljme.runtime.cldc.debug.Debugging;
import cc.squirreljme.runtime.lcdui.mle.fb.FBUIBackend;
import cc.squirreljme.runtime.lcdui.mle.fb.NativeFBAttachment;
import cc.squirreljme.runtime.lcdui.mle.headless.HeadlessAttachment;
import cc.squirreljme.runtime.lcdui.mle.pure.NativeUIBackend;

/**
 * Used to gain access to the {@link UIBackend}.
 *
 * @since 2020/07/19
 */
@SquirrelJMEVendorApi
public final class UIBackendFactory
{
    /**
     * {@squirreljme.property cc.squirreljme.runtime.lcdui.mle.fallback=bool
     * Force the usage of the fallback UIForm in the event that native form
     * handling should NOT be used.}
     */
    @SquirrelJMEVendorApi
    public static final String FORCE_FALLBACK_PROPERTY =
        "cc.squirreljme.runtime.lcdui.mle.fallback";
    
    /**
     * {@squirreljme.property cc.squirreljme.runtime.lcdui.mle.headless=bool
     * Force that the headless UIForm be used, this will mean that nothing
     * will be displayed on the screen.}
     */
    @SquirrelJMEVendorApi
    public static final String FORCE_HEADLESS_PROPERTY =
        "cc.squirreljme.runtime.lcdui.mle.headless";
    
    /** The instance of the form engine to be used. */
    @SuppressWarnings({"StaticVariableMayNotBeInitialized", 
        "NonConstantFieldWithUpperCaseName"})
    private static UIBackend _DEFAULT;
    
    /**
     * Gets an instance of the UI engine.
     * 
     * @param __allowHeadless Allow a headless display to be used?
     * @return The instance of the engine to use.
     * @since 2020/06/30
     */
    @SuppressWarnings("StaticVariableUsedBeforeInitialization")
    @SquirrelJMEVendorApi
    public static UIBackend getInstance(boolean __allowHeadless)
    {
        // If this was already cached, use that
        UIBackend rv = UIBackendFactory._DEFAULT;
        if (rv != null)
            return rv;
        
        // Debug
        Debugging.debugNote("Initializing UIFormEngine...");
        
        // These are properties which determine which kind of engine can be
        // returned
        boolean forceFallback = Boolean.getBoolean(
            UIBackendFactory.FORCE_FALLBACK_PROPERTY);
        boolean forceHeadless = Boolean.getBoolean(
            UIBackendFactory.FORCE_HEADLESS_PROPERTY);
        boolean isForcing = (forceFallback || forceHeadless);
        
        // Use native forms if supported unless we are forcing other options
        UIDisplayBracket[] displays = UIFormShelf.displays();
        if (displays != null && displays.length > 0 &&
            0 != UIFormShelf.metric(displays[0],
                UIMetricType.UIFORMS_SUPPORTED) && 
            !isForcing)
            rv = new NativeUIBackend();
        
        // Otherwise, use the fallback implementation (raw framebuffer)
        else
        {
            // TODO: For now only force headless as FB UI is not implemented
            if (!forceHeadless)
            {
                Debugging.todoNote("Undo force of headless for FB UI.");
                forceHeadless = true;
            }
            
            // Use a headless interface? This is if we have no framebuffer
            // and the only have to have graphics is to fake it
            if (forceHeadless)
            {
                /* {@squirreljme.error EB33 Headless display not permitted
                at this current time.} */
                if (!__allowHeadless)
                    throw new IllegalStateException("EB33");
                
                // Emit a notice
                Debugging.notice("Framebuffer either does not exist " +
                    "or is disabled, attaching without a head.");
                
                // Create it
                rv = new FBUIBackend(new HeadlessAttachment(
                    UIPixelFormat.INT_RGB888, 240, 320));
            }
            
            // Use a method that uses the backing framebuffer here instead
            else
                rv = new FBUIBackend(new NativeFBAttachment());
        }
        
        // Cache and use
        UIBackendFactory._DEFAULT = rv;
        return rv;
    }
}