That sounds like bi-linear filtering to me. No way to turn that off at the moment. It has been requested though, so you never know what future updates might allow.
In the meantime try making the texture bigger, or... Theres a neat thing you can do if you are masking textures and bearing in mind you can have the maskcolor any color you like if you are using the read/write pixel method. Taking your white circle as an example set the background color to 254,254,254 say, then mask out this nearly white part. Now the bilinear filtering will be much less obvious on the white circle that remains. In general use mask colors that are close to but not the same as the colors that will be left after masking if you want this sort of effect.
This gives the general idea. I am being a bit naughty here by drawing directly to the texture. It usually works ok though, but the recommended method of writing to textures is by sole use of readpixel/writepixel.
In the meantime try making the texture bigger, or... Theres a neat thing you can do if you are masking textures and bearing in mind you can have the maskcolor any color you like if you are using the read/write pixel method. Taking your white circle as an example set the background color to 254,254,254 say, then mask out this nearly white part. Now the bilinear filtering will be much less obvious on the white circle that remains. In general use mask colors that are close to but not the same as the colors that will be left after masking if you want this sort of effect.
This gives the general idea. I am being a bit naughty here by drawing directly to the texture. It usually works ok though, but the recommended method of writing to textures is by sole use of readpixel/writepixel.
texture=CreateTexture(128,128,4) SetBuffer TextureBuffer(texture) maskred=254 : maskgreen=0 : maskblue=0 maskrgb=maskred Shl 16 Or maskgreen Shl 8 Or maskblue Color maskred,maskgreen,maskblue Rect 0,0,128,128 Color 255,0,0 For i = 0 To 128 Step 16 Rect i,0,1,128 Rect 0,i,128,1 Next For i=0 To 127 For j=0 To 127 argb=ReadPixel(i,j,TextureBuffer(texture)) rgb= argb And $FFFFFF If rgb=maskrgb Then alpha=0 Else alpha=255 WritePixel i,j,alpha Shl 24+rgb,TextureBuffer(texture) Next Next