Folks,
I understand that I can load images with LW. How do I prepare this
image afterwards for rendering with OpenGL? Or more precisely, how do
I convert the image into something suitable for passing to
glu-build2-dmipmaps?
I'm looking to simply render a JPEG or PNG using OpenGL.
Thanks, Joel
On Tue, 11 Jan 2005 13:26:38 +0000, joel reymont <joelr1@gmail.com> wrote:
> [...]
> I'm looking to simply render a JPEG or PNG using OpenGL.
I can probably narrow this down a bit... The icosahedron example uses
gl-tex-image2-d to render a gl-vector. The vector is defined in lisp
code as a sequence of hex values.
I understood from browsing the list archives that I would need to use
some C/C++ library to extract the pixel values as RGBA and stick them
one by one into a gl-vector. Then I could free the image itself. If I
were to stick the RGBA data into a texture then I would need to free
the gl-vector afterwards.
I also saw the discussion about optimizing dotimes when used to copy
the pixel values. Is there a way to get the RGBA values from CAPI? Is
using an external library and populating a gl-vector the way to go?
Thanks, Joel
Here I go answering my own questions... :-)
On Tue, 11 Jan 2005 14:46:50 +0000, joel reymont <joelr1@gmail.com> wrote:
> [...]
> I understood from browsing the list archives that I would need to use
> some C/C++ library to extract the pixel values as RGBA and stick them
> one by one into a gl-vector.
I suppose this cannot be avoided as OpenGL functions do expect a gl-vector.
> I also saw the discussion about optimizing dotimes when used to copy
> the pixel values.
I suppose an optimized loop will be needed to populate the vector.
> Is there a way to get the RGBA values from CAPI? Is
> using an external library and populating a gl-vector the way to go?
My only requirement is to load a "skin pack" from disk so linking to
something like Image Magick would be an overkill. I also got some
interesting info from LispWorks tech support.
Apparently, Windows does not support alpha blending and so LW needs to
convert images to BMP for drawing and BMP does not have an alpha
channel. Historically, images that I use were always two-part: one
file for the image itself and one file for the mask. The mask is a
grayscale image where the value of R, G or B is the alpha value for
the corresponding image. It's fairly straightforward to separate an
RGBA image into RGB and A if you are using Photoshop.
You can use a sequence like this in the REPL to get the pixel value:
(setf pane (make-instance 'capi:output-pane
:width 300
:height 400))
(capi:contain pane)
(setf external-image (gp:read-external-image "~/temp/lobby.jpg")
image (gp:load-image pane external-image :force-plain t))
(setf access (gp:make-image-access pane image))
(gp:image-access-transfer-from-image access)
(setf width (gp:image-access-width access))
(setf pixel (gp:image-access-pixel access 10 10))
You can then retrieve the color like this:
(setf color (color:unconvert-color pane pixel))
And the individual component values like this:
(setf red-byte (* (color:color-red color) 255))
There are also color:color-blue, color:color-green and color:color-alpha.
The values need to be truncated and made to occupy one byte which is
something that I have to investigate as I'm new to Common Lisp. Any
takers?
Thanks, Joel
I forgot to add that to figure out your alpha value you just take either the red, gree or blue component of the color at matching X,Y f your mask image and stick that as every 4th byte into your gl-vector. Might be obvious but just in case... :-)
Unable to parse email body. Email id is 3395
On Tue, 11 Jan 2005 21:26:25 GMT, davef@lispworks.com
<davef@lispworks.com> wrote:
> [...]
> > The values need to be truncated and made to occupy one byte which is
> > something that I have to investigate as I'm new to Common Lisp. Any
> > takers?
>
> See the Common Lisp function TRUNCATE.
This is taken from texture.lisp in the opengel examples:
(defun get-icosahedron-texture-data ()
(when temp-icosahedron-texture-data
(setq *icosahedron-texture-data*
(opengl:make-gl-vector :unsigned-8 (* 64 64 4)
:contents
temp-icosahedron-texture-data)
temp-icosahedron-texture-data nil ;; free the data
)
)
*icosahedron-texture-data*)
If I pass a list of short floats known to be < 255 as contents would
the floats be truncated to bytes automatically? Would there be a
performance penalty?
I would like to create a function that returns a gl-vector of RGBA
data given either image and mask files or just the image file. I have
high number of images set up as image/mask pairs and so I'll be using
this routine a lot. Once the images are converted to OpenGL textures I
won't be using the routines anymore so I'm inclined to think that
coding this routine in Lisp would be ok.
Also, my lobby JPEG is 794x538 and 264k big. It looks like I would
need to either push the bytes into the list and then reverse it before
passing it as :contents to make-gl-vector or set the individual
vectore elements are I go. Which approach is best (fastest?) given
that the lobby JPEG is my biggest image?
Thanks, Joel