How To ... Create a MonoChrome RenderEffect(如何创建灰度渲染效果)

How To ... Create a MonoChrome RenderEffect

MAXScript:



plugin RenderEffect MonoChrome

name:
"MonoChrome"

classID:#(0x9e6e9e77, 0xbe815df4)

(

rollout
about_rollout
"About..."

(

label about_label
"MonoChrome Filter"

)

on
apply r_image progressCB:
do

(

progressCB.setTitle
"MonoChrome Effect"

local
oldEscapeEnable = escapeEnable

escapeEnable = false

bmp_w = r_image.width

bmp_h = r_image.height

for
y = 0
to
bmp_h-1
do

(

if
progressCB.progress y (bmp_h-1)
then
exit

pixel_line = getPixels r_image [0,y] bmp_w

for
x = 1
to
bmp_w
do

(

p_v
= pixel_line[x].value

pixel_line[x] = color p_v p_v p_v pixel_line[x].alpha

)--end x loop

setPixels r_image [0,y] pixel_line

)
--end y loop

escapeEnable = oldEscapeEnable

)
--end on apply

)
--end plugin

 
 

Step-By-Step:

plugin RenderEffect MonoChrome


name:"MonoChrome"


classID:#(0x9e6e9e77, 0xbe815df4)


(


A
scripted plug-in starts with the constructor plugin

followed by the superclass of the scripted plug-in (
renderEffect

) and the class name of
the plug-in (
MonoChrome

). In addition, we have
to provide the name

which will appear in the effects list, and a unique classID

.

The
classID

is used by 3ds
Max

to
recognize the plug-in class when loading the scene. To generate a new unique ID,
you can use the GenclassID

() method in the Listener
and copy the result into the script.

To keep
all versions of this plug-in compatible around the world, it is recommended to
copy the above classID though.

Scripted
Plug-ins

Scripted RenderEffect
Plug-ins

classID

rollout about_rollout "About..."


(


label about_label "MonoChrome Filter"


)


The
plug-in will have no controls. We will create a very simple rollout containing a
single line of text just to show the user he has loaded something.

Rollout
Clauses

Label

on
apply r_image progressCB: do


(


A
renderEffect plug-in has a main handler which will be executed each time the
effect is applied to the image. The image buffer of the renderer will be passed
as the only parameter to the handler - we use a user variable named
r_image

which will contain the image we will work on. Also, we define a progress
callback object in order to update the main renderer progress bar while
processing the image.

Scripted RenderEffect
Plug-ins

RenderEffect Progress
Callback Mechanism

progressCB.setTitle "MonoChrome Effect"


Using
the setTitle

method in the progressCB

object, we define the
name to be displayed in the Rendering Effect progress window resp. the Renderer
Progress window during processing. In the former case, the line will read
"Currently Updating: MonoChrome Effect". In the latter case, the line will read
"Current Task: MonoChrome Effect".

RenderEffect Progress
Callback Mechanism

local oldEscapeEnable = escapeEnable


escapeEnable = false


In order
to be able to capture and process the pressing of the Escape key during the main
loop of the effect without actually breaking the script execution, we will have
to disable the MAXScript Escape key handling. For this purpose we will store the
current state of the Escape handling (
true

or false

) in a temporary user variable and then assign false

to the MAXScript System Global
variable controlling the Escape handling

. Later on, after the
main loop, we will set it back to its original state stored in the
oldEscapeEnable

user
variable.

bmp_w = r_image.width


We will
need the width

of the rendered image. We store the .width

property of the image in the user variable bmp_w

.

bmp_h = r_image.height


We will
also need the height

of the rendered image. We store the .height

property of the image in the user variable bmp_h

.

bitmap.height

for y = 0 to bmp_h-1 do


(


We will
loop through all lines in the image. Image pixel access requires 0-based
indexing, this means the upper left pixel of a 640x480 image has coordinates
[0,0] and the bottom right pixel has coordinates [639,479]. The variable
y


will be assigned the values from 0 to the height of the image minus 1 each time
the for loop repeats itself.

For Loop

if
progressCB.progress y (bmp_h-1) then exit


This
line does two things:

Since
the .
progress

method of the progress callback object returns true

when the user has pressed Escape and false

otherwise, we check the return value and exit the loop when
true

is returned. This will bring us to the line after the end of the
y


loop.

The same
method also accepts two arguments ?the current value and the max. value needed
to calculate the progress percentage. In our case, we supply the current line
and the total number of lines. For example, if we are on line 300 and the bitmap
has 600 lines, the progress bar will show 50% done...

RenderEffect Progress
Callback Mechanism

Loop Exit

pixel_line = getPixels r_image [0,y] bmp_w


The
getpixels

function reads pixels from the specified file starting at the position
supplied by the Point2 value and reads the number of pixels specified by the
last value. The result will be assigned as array to the user variable
pixel_line

. We start reading at the
first pixel to the left and read all bmp_w

pixels - a whole scanline contains as many pixels as the width of the
image.

getPixels

for x = 1 to bmp_w do


(


Now we
can loop through all values in the array of pixel values. Because arrays in
MAXScript are 1-Based, we count from 1 to the width of the image.

For Loop

p_v = pixel_line[x].value


pixel_line[x] = color p_v p_v p_v pixel_line[x].alpha


This is
the actual core of the code - we get the .Value property of the color (its
greyscale intensity) and generate a new color value with Red, Green and Blue
values equal to the .Value of the original pixel. To keep the alpha channel
untouched, we just add the original alpha value to the RGBA color. We store the
result at the same position in the array and thus overwrite the color
information with a grayscale version!

Color
Values

)--end x loop


setPixels r_image [0,y] pixel_line


After
processing all pixels of a scanline, the setpixels

function writes the array pixel_line

containing the new
grayscale values back into the image starting at the same position. This
overwrites the colors in the current line y

.

setPixels

)--end y loop


We are
ready with the loops and the whole bitmap has been changed. The on
apply


handler will return the resulting bitmap to the system and it will be shown in
the Virtual Frame Buffer.

escapeEnable = oldEscapeEnable


As
mentioned before, we will have to set the MAXScript Escape key handling to its
original state before the render effect loop.

)--end on apply


)--end plugin

Using the Script

After
evaluating the script, a new plug-in effect called "MonoChrome" will appear on
the Renderer > Effects... > Add... list. Add it to the effects queue and
render the scene. The result will be a monochrome version of the rendering. Note
that scripted renderEffects are relatively slow compared to "real" plug-ins
written with the SDK, but are very flexible and fast to prototype.

In the
Virtual Frame Buffer, you can take a look at the Alpha and Monochrome version of
the image - the Alpha should be unchanged, and the Monochrome version should be
identical to the RGB image generated by the renderEffect.

Where to go from here

A
relatively easy change to this basic script would be the change of only every
Nth line of the bitmap. By just adding a by
2

option
to the for y loop you will affect only every second line!

for y = 0 to bmp_h-1 by 2 do


Adding
by
2

to the
x loop too will affect only a grid of pixels! You could play with values higher
than 2, or even add UI controls for user-defined line and pixel
steps.

A more
complex change to the script would be the tinting of the monochrome image by
using different proportions of the monochrome value in the R, G and B channels.
To do this, you could add a rollout and a paramBlock defining 3 Float values and
let the user specify how much of each channel to be used. Then multiply the p_v
value by the 3 values while assigning them to the R, G and B values of the
image.