com.github.mathiewz.slick.opengl.SlickCallable Maven / Gradle / Ivy

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The main purpose of this libraryis to modernize and maintain the slick2D library.
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package com.github.mathiewz.slick.opengl;

import org.lwjgl.opengl.GL11;

import com.github.mathiewz.slick.opengl.renderer.Renderer;

/**
 * A utility to allow performing GL operations without contaminating the
 * Slick OpenGL state. Note this will not protect you from OpenGL programming errors
 * like a glBegin() without a glEnd(), or glPush() without glPop() etc.
 *
 * Expected usage:
 *
 * 
 * SlickCallable callable = new SlickCallable() {
 * 	   public performGLOperations() {
 * 			GL.glTranslate(0,0,1);
 * 			glBegin(GL.GL_POLYGONS);
 *  			glVertex(..);
 *              ...
 *          glEnd();
 *     }
 * }
 * callable.call();
 * 
 *
 * Alternatively you can use the static methods directly
 *
 * 
 * SlickCallable.enterSafeBlock();
 *
 * GL.glTranslate(0,0,1);
 * glBegin(GL.GL_POLYGONS);
 *     glVertex(..);
 *     ...
 * glEnd();
 *
 * SlickCallable.leaveSafeBlock();
 * 
 *
 * @author kevin
 */
public abstract class SlickCallable {
    /** The last texture used */
    private static Texture lastUsed;
    /** True if we're in a safe block */
    private static boolean inSafe = false;

    /**
     * Enter a safe block ensuring that all the OpenGL state that slick
     * uses is safe before touching the GL state directly.
     */
    public static void enterSafeBlock() {
        if (inSafe) {
            return;
        }

        Renderer.get().flush();
        lastUsed = TextureImpl.getLastBind();
        TextureImpl.bindNone();
        GL11.glPushAttrib(GL11.GL_ALL_ATTRIB_BITS);
        GL11.glPushClientAttrib(GL11.GL_ALL_CLIENT_ATTRIB_BITS);
        GL11.glMatrixMode(GL11.GL_MODELVIEW);
        GL11.glPushMatrix();
        GL11.glMatrixMode(GL11.GL_PROJECTION);
        GL11.glPushMatrix();
        GL11.glMatrixMode(GL11.GL_MODELVIEW);

        inSafe = true;
    }

    /**
     * Leave a safe block ensuring that all of Slick's OpenGL state is
     * restored since the last enter.
     */
    public static void leaveSafeBlock() {
        if (!inSafe) {
            return;
        }

        GL11.glMatrixMode(GL11.GL_PROJECTION);
        GL11.glPopMatrix();
        GL11.glMatrixMode(GL11.GL_MODELVIEW);
        GL11.glPopMatrix();
        GL11.glPopClientAttrib();
        GL11.glPopAttrib();

        if (lastUsed != null) {
            lastUsed.bind();
        } else {
            TextureImpl.bindNone();
        }

        inSafe = false;
    }

    /**
     * Cause this callable to perform it's GL operations (@see performGLOperations()). This
     * method will block until the GL operations have been performed.
     *
     */
    public final void call() {
        enterSafeBlock();

        performGLOperations();

        leaveSafeBlock();
    }

    /**
     * Perform the GL operations that this callable is intended to. This operations should
     * not effect the slick OpenGL state.
     *
     */
    protected abstract void performGLOperations();
}