                                   Graphics Overview

    Dive into Demo Index to learn.

    The order layers are drawn on top of each other is:

    /* Graphics Not Rendered in HTML */

    * See GrUpdateScrn(), GrUpdateTasks() and GrUpdateTaskWin() called by the WinMgr
    task 30fps.  Notice the task's draw_it() callback being called.  Only tasks on C
    ore0 are allowed to have windows.  There is one window per task, no child
    windows.  You can have pop-up child tasks.

    * CDCs (device contexts) are a data type for controlling graphics on the scrn or
    graphics in mem.  The device context structure has thick and color.  You use
    DCAlias() to create your own structure, with its own color and thick.  Free it
    with DCDel() when finished.

    * gr.dc is a device context for persistent data on the scrn, not needing to be
    redrawn.  You create an alias for this by using DCAlias() and work with that.
    See ::/Demo/Graphics/NetOfDots.HC.

    * There are various flavors of line and point plotting routines.  GrLine() and
    GrPlot() are the simplest.  The others allow 3D graphics and rotations.

    * See ::/Doc/Transform.DD for adding a transformation.

    * You change the Fs->draw_it var to point to your DrawIt() function which gets
    called each scrn refresh (30 fps).  You draw everything in the window over and
    over again.  See ::/Demo/Graphics/Box.HC.

    * Use the graphic sprite resource editor, <CTRL-r>, to create a sprite that can
    be plotted with Sprite3() or output to the cmd line with Sprite().  Use $IB,"",B
    I=1$ in a src program to insert the addr of sprite binary data item #1.  To
    learn how the numbers work, after creating a sprite with <CTRL-r>, toggle to
    plain text with <CTRL-t> and check its num.  Make an assignment to a ptr var or
    pass to Sprite3() with $IB,"",BI=n$.  Use <CTRL-r>'s "Pointer to Sprite" to make
    a $IB...$ entry.  See ::/Demo/Graphics/SpritePlot.HC and
    ::/Demo/Graphics/SpritePlot3D.HC.  The origin (zero point) for a sprite is
    defined by the cursor location when you pressed <CTRL-r> to make it.  You can
    edit a sprite by clicking the cursor on it and pressing <CTRL-r> again.

    * Set DCF_SYMMETRY in the CDC.flags and call DCSymmetrySet() or DCSymmetry3Set()
    .  This will plot a mirror image in addition to the primary image.  Set
    DCF_JUST_MIRROR to plot just the image, but this required DCF_SYMMETRY to be set
    at the same time.  Note: You can only have one symmetry active at a time
    including in CSprites.

    * Use DCNew() to create a mem bitmap which can be used to work off-scrn and
    which can be GrBloted onto the scrn.  If you set brush member of CDC to another
    CDC, all the graphic routines will GrBlot() the brush instead of GrPlot().  See
    ::/Demo/Graphics/Blot.HC.

    * There are a few raster operations available.  They go in bits 8-11 of the dc->
    color member var which is a CColorROPU32.  ROP_COLLISION is special.  It counts
    the num of pixs drawn on non-background locations.  Using ROP_COLLISION with
    vector CSprite's is tricky because overlapping pixs from lines in the CSprite
    reg as collisions.  You can either work with a nonzero count or convert your
    CSprite to a bitmap if your subelements draw on top of each other.  Be sure to
    set ->bkcolor before using ROP_COLLISION.  See ::/Demo/Graphics/Collision.HC and
    Titanium.

    * The ->dither_probability_u16 member of CDC is a U16 used to statistically sel
    between two colors to get something resembling more shades of color.  See
    ::/Demo/Graphics/SunMoon.HC and ::/Demo/Graphics/Shading.HC.  It works with many
    graphic routines, but not those with pens.

    * There is a mechanism built-in for generating motion based on differential
    equations, which allows realistic physics.  You create an CMathODE struct with
    ODENew(), passing it the num of vars in the state vect.  For realistic physics,
    you usually have 2 state vars for each dimension (for each mass) because motion
    is governed by F=mA which is a 2nd order equation.  The two states are pos and
    velocity and to solve these you need to supply the derivative of pos and
    velocity.  The derivative of pos is usually simply the current velocity and the
    derivative of velocity is the acceleration (the sum of forces on a mass divided
    by mass).  To help provide meaningful names for values in the state vect, you
    can create an COrder2D3 ptr and point it to a mass in the state vect.  Six
    elements in the state vect are required for each mass.

    See Math/CMathODE.
    See ::/Demo/Games/Rocket.HC.