Messages from Usenet group comp.lang.idl-pvwave, compiled by Paulo Penteado
I have two IDLgrPoly objects, one inside of the other. I have mapped a JPEG image on the outer object and would like to use alpha blending to adjust the opacity of the outer object so you can see through it to the inner object. I read the JPEG, adjust the array to add a 4th channel and assign all elements of that channel a value of say 100. (I am assuming that the alpha channel ranges from 0..255) I then create the Image and polygon objects like so: oImage = OBJ_NEW('IDLgrImage', image, INTERLEAVE=2, $ BLEND_FUNCTION=[3,4], /INTERPOLATE) state.oFBSurface = OBJ_NEW("IDLgrPolygon", TRANSPOSE([[x],[y],[z]]), $ SHADING=1, POLY=mesh, COLOR=[255,255,255], $ TEXTURE_MAP=oImage, STYLE=2, /TEXTURE_INTERP, $ TEXTURE_COORD=TRANSPOSE([[ynorm],[znorm]]), $ ZERO_OPACITY_SKIP=0) What I get is an object with my image mapped to it in where the final image is a function of the original image, the IDLgrWindow's background color and the values in my alpha channel. In other words, the image fades out to the background color, but you still can't see what is "inside" or behind the poly. I can't see the axes which fall inside my outer object nor can I see the inner object. Am I approaching this correctly? Can you adjust the opacity of the texels so you can see other objects behind them in a scene? Thanks for any help! -Rick Towler