Z‑buffer Output

Reference Guide > Output Devices and Window Systems > Z‑buffer Output

Z‑buffer Output

The Z-buffer allows you to create complex 3D plots, image warping to polygons, and transparency effects without special hardware.

To direct graphics output to the Z-buffer, enter the command:

SET_PLOT, 'Z'

This causes PV‑WAVE to use the Z-buffer driver for producing graphical output. Once the Z-buffer driver is enabled via SET_PLOT, the DEVICE procedure is used to control its actions, as described in "Controlling Z-buffer Output with DEVICE Keywords".

Use INFO, /Device to view the driver’s current settings.

Controlling Z-buffer Output with DEVICE Keywords

The following keywords to the DEVICE procedure provide control of the Z-buffer driver:

Close—Deallocates the memory used by the buffers. The Z-buffer device is reinitialized if subsequent graphics operations are directed to the device.

Get_Graphics_Function—See the description of the Get_Graphics_Function keyword in "Controlling X Driver with DEVICE Keywords".

Get_Write_Mask—See the description of the Get_Write_Mask keyword in "Controlling X Driver with DEVICE Keywords".

Set_Character_Size—A two-element vector that changes the standard width and height of the vector-drawn fonts. The first element in the vector contains the new character width, and the second element contains the height. By default, characters are approximately 8-pixels wide, with 12 pixels between lines.

Set_Colors—Sets the number of pixel values, !D.N_Colors. This value is used by a number of routines to determine the scaling of pixel data and the default drawing index. Allowable values range from 2 to 256, and the default value is 256. Use this parameter to make the Z-buffer device compatible with devices with fewer than 256 color indices.

Set_Graphics_Function—See the description of the Set_Graphics_Function keyword in "Controlling X Driver with DEVICE Keywords".

The Z-buffer allows you to use all graphics functions supported by the X driver.

Set_Resolution—Two-element vector that sets the width and height of the buffers. The default size is 640-by-512. If this size is not the same as the existing buffers, the current buffers are destroyed and the device is reinitialized.

Set_Write_Mask—See the description of the Set_Write_Mask keyword in "Controlling X Driver with DEVICE Keywords".

Z-buffer Examples

Example 1

This example demonstrates how graphics can be rendered in memory (into the Z-buffer) and then later displayed. The resulting image is shown in Image Rendered from Z-Buffer.

SET_PLOT, 'z'

SHADE_SURF, HANNING(23,23)

SURFACE, HANNING(23,23), /Noerase

img = TVRD(0,0,640,512)

SET_PLOT, 'x'

TV, img

Figure B-6: Image Rendered from Z-Buffer

Example 2

This example creates a single image composed of two intersecting objects drawn with hidden surfaces removed. This effect can only be accomplished with the Z-buffer. The resulting image is shown in Figure B-7: Image Composed of two Intersecting Objects on page 2131.

; Remember current graphics device

dev_name = !D.Name

im = BYTARR(512,512)

; Open the file containing the image.

OPENR, 1, FILEPATH('mandril.img', SubDir='data' )

READU, 1, im

CLOSE, 1

SET_PLOT, 'z'

; Erase the Z-buffer in case there was something in there before.

ERASE

; Draw a surface. Remember the 3D viewing transform (/Save).

SHADE_SURF, HANNING(23,23), /Save

; Create a 3D quadrilateral in data coordinates.

verts=[ [0,0,0], [20,0,0.5], [20,20,1], [0,20,0.5] ]

; Draw the transformed quadrilateral with an image mapped

; onto it.

POLYFILL, Verts, Pattern = im, $

   Image_coord=[[0,0],[511,0],[511,511], [0,511]], /T3d

res = TVRD(0,0,640,512)

SET_PLOT, dev_name

TVSCL, res

; Notice how the two objects intersect.

Figure B-7: Image Composed of two Intersecting Objects

Example 3

In this example, the same image from the previous example is created; however, this time maximum intensity projection is used to produce a transparency effect. The resulting image is shown in Image with Transparency Effect.

; Remember current graphics device

dev_name = !D.Name

im = BYTARR(512,512)

OPENR, 1, FILEPATH('mandril.img', SubDir='data' )

READU, 1, im

CLOSE, 1

SET_PLOT, 'z'

; Erase the Z-buffer in case there was something in there before.

ERASE

; Draw a surface.

; Remember the 3D viewing transform (/Save).

SHADE_SURF, HANNING(23,23), /Save

; Create a 3D quadrilateral in data coordinates.

verts=[ [0,0,0], [20,0,0.5], [20,20,1], [0,20,0.5] ]

; Draw the transformed quadrilateral with an image mapped onto

; it.

POLYFILL, Verts, Pattern = im, $

   Image_coord=[[0,0],[511,0],[511,511], [0,511]], /T3d, /Mip

res = TVRD(0,0,640,512)

SET_PLOT, dev_name

; Notice how the two objects interact this time. You can partially

; see through the surface to the image passing through it.

TVSCL, res

Figure B-8: Image with Transparency Effect

Version 2017.0