Set_Camera_By_Volume

Functions
void	Set_Camera_By_Volume (const char *projection, double xmin, double xmax, double ymin, double ymax)
void	QSet_Camera_By_Volume (const char *segment, const char *projection, double xmin, double xmax, double ymin, double ymax)

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Function Documentation

void Set_Camera_By_Volume	(	const char *	projection,
		double	xmin,
		double	xmax,
		double	ymin,
		double	ymax
	)

Sets up the Camera so that the screen will show one simple rectangular box extracted from the infinite user data space.

Parameters:

	projection	- Special constant---either "perspective", "orthographic", "stretched", or an "oblique" form (see below). Can be uppercase, lowercase, or any mixture.
	xmin	- Minimum limit along the X-axis, of what will visible.
	xmax	- Maximum limit along the X-axis, of what will visible.
	ymin	- Minimum limit along the Y-axis.
	ymax	- Maximum limit along the Y-axis.

DETAILS

There are two major methods of determining how much of your scene is going to be visible on the screen--- Set_Camera_By_Volume() , and the threesome of Camera Position, Camera Target, and Camera Field (or the general Set_Camera() ). Set_Camera_By_Volume() simplifies things by making some assumptions about the Z-axis. It also defines the field of view in terms of box, which might be more convenient for you, rather than in terms of a center and a radius.

Projection tells the system how to flatten your scene into 2-D and how to pack it into the available screen window. Choices for projection include:

• perspective

  Generally used for 3-D realistic scenes. The system will arrange that at least as much of your scene as is specified by the (xmin, xmax, ymin, ymax) camera volume will appear on the screen. If the screen window's height-to-width ratio (the "aspect" ratio) is a bit different than the camera volume's, then you'll be able to see a little extra of your scene on the margins.

• orthographic

  Generally used for 2-D scenes where you want to maintain the aspect ratio, or for 3-D engineering or architectural drawings. As with "perspective", the system will arrange that at least as much of your scene as is specified by the camera volume will appear on the screen. Depending on the aspect ratios, you may be able to see a little more of your scene than you asked for on the left and right or on the top and bottom.

• stretched

  Generally used for 2-D pictures where it's important that the camera box completely and exactly fill the available screen window, no matter what the camera and window aspect ratios are. The system first does an orthographic projection, then stretches the projection (possibly asymmetrically) to fill the screen window. A typical use would be for a potentiometer display on a menu, where you don't want to worry about the size and shape of the window provided. This can be handy, but note that the stretching process may turn shapes such as circles into ellipses!

• oblique orthographic

  Similar to orthographic except that the projection has been skewed in the traditional style of mechanical drafting. Orthographic has the problem that objects viewed head-on in wire-frame tend to have their backs and fronts collapsed together. Oblique spreads the back out from the front in a uniform way, keeping equal lengths equal (unlike a perspective projection.) The oblique projection takes one or two floating-point constants---the angle in degrees to skew by in X and Y. See Set_Camera_Projection() for more details.

• oblique perspective

  Similar to perspective except that the projection (or the projection plane) has been skewed. It is useful for off-center viewing, as when doing stereo projections. See Set_Camera_Projection() for more details.

The arguments that Set_Camera_By_Volume() passes to Set_Camera() are as follows: the camera projection is passed straight through, the up vector is set to (0.0, 1.0, 0.0), the field is set to max ( xmax - xmin, ymax - ymin ), the target is set to

and the camera position is set to

The "-2.5" is chosen so the view will be reasonable if you've chosen a perspective projection, or if you later toggle to a perspective projection.

NOTES

For historical reasons the words for the regular projections can be abbreviated. The oblique projections cannot be abbreviated.

RESTRICTIONS

See also:

Set_Camera, Set_Camera_Field, Set_Camera_Position, Set_Camera_Projection, Set_Camera_Target, Set_Camera_Up_Vector, Zoom_Camera, Orbit_Camera, Pan_Camera, Dolly_Camera, Roll_Camera, Set_Window, Translate_Object, Rotate_Object.

void QSet_Camera_By_Volume	(	const char *	segment,
		const char *	projection,
		double	xmin,
		double	xmax,
		double	ymin,
		double	ymax
	)

Similar to Set_Camera_By_Volume(), but operates on a given segment rather than the currently open one. Operates with a color values rather than names or map indices.

Parameters:

	segment	- Name of the segment(s) to be changed.
	projection	- Special constant---either "perspective", "orthographic", "stretched", or an "oblique" form (see below). Can be uppercase, lowercase, or any mixture.
	xmin	- Minimum limit along the X-axis, of what will visible.
	xmax	- Maximum limit along the X-axis, of what will visible.
	ymin	- Minimum limit along the Y-axis.
	ymax	- Maximum limit along the Y-axis.

DETAILS

No additional details. See Set_Camera_By_Volume()