Sprite Transparency problem

Try playing with this section of code:

glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glEnable(GL_ALPHA_TEST);
glAlphaFunc(GL_GREATER, 0);

basically, mess with the zero, try changing it to a one. and make sure you delete every other blending command first. The lines are caused by texture streching and the wrap around can be fixed by a "GL_CLAMP" (if I remember correctly) instead of GL_WRAP at texture creation. (again if I remember correctly for that constant as well).

Let me know if it works!!

Quote:

Original post by RunningInt It seems that anti-aliasing is likely causing this problem. I was wondering if there is some simple solution to this.

Close, but not quite right. Your problem is texture filtering - red pixels may have an alpha of zero after conversion, but the interpolation at the sprite edges means you get part alpha and part red edges. There are a couple of ways to fix it:

1. Disable texture filtering (or more accurately, switch the MAG_FILTER to NEAREST). This of course means you get a pixely enlargement rather than the smoothed version you've got now.

2. Don't scale the sprite, use the sprite at its proper size. This really is just a way of getting no filtering though.

3. The proper way - ditch the hacky conversion with a colour key and create and load proper RGBA files from disk. Use an image library if you don't want to rewrite yet another png/etc. loader.

To fix the foot wrapping thing, specify CLAMP_TO_EDGE (not CLAMP!) for your GL_TEXTURE_WRAP_S and GL_TEXTURE_WRAP_T parameters.

if u disable GL_BLEND your set..

forget glblend. it doesnt exempt the sprite from the zbuffer and in this picture of yours has no function.

By using just glalpha you will get a nice effect.

Drop me ur email ill send u my own 2d application and you can see how nice it looks close up if you use GL_ALPHA and dump GL_BLEND



[Edited by - phantom on November 28, 2005 9:55:41 PM]

Quote:

Original post by OrangyTang Quote: Original post by RunningInt It seems that anti-aliasing is likely causing this problem. I was wondering if there is some simple solution to this. Close, but not quite right. Your problem is texture filtering - red pixels may have an alpha of zero after conversion, but the interpolation at the sprite edges means you get part alpha and part red edges. There are a couple of ways to fix it: 1. Disable texture filtering (or more accurately, switch the MAG_FILTER to NEAREST). This of course means you get a pixely enlargement rather than the smoothed version you've got now. 2. Don't scale the sprite, use the sprite at its proper size. This really is just a way of getting no filtering though. 3. The proper way - ditch the hacky conversion with a colour key and create and load proper RGBA files from disk. Use an image library if you don't want to rewrite yet another png/etc. loader. To fix the foot wrapping thing, specify CLAMP_TO_EDGE (not CLAMP!) for your GL_TEXTURE_WRAP_S and GL_TEXTURE_WRAP_T parameters.

Thanks this fixes the problem. I just switched the mag_filter to nearest. I am making a total war like game, so the units can be blocky, and I guess there is a slight speed advantage with using nearest rather than linear.

I am actually loading RGBA files from disk. I have no paint program that can create bitmaps with alpha channel so I made a program to convert an RGB bitmap file into a raw ARGB data file using a key color.

I had to use GL_CLAMP as I don't seem to have CLAMP_TO_EDGE defined. Is there a problem with GL_CLAMP?

Quote:

Original post by arbuckle911 Try playing with this section of code: glEnable(GL_BLEND); glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); glEnable(GL_ALPHA_TEST); glAlphaFunc(GL_GREATER, 0); basically, mess with the zero, try changing it to a one. and make sure you delete every other blending command first. The lines are caused by texture streching and the wrap around can be fixed by a "GL_CLAMP" (if I remember correctly) instead of GL_WRAP at texture creation. (again if I remember correctly for that constant as well). Let me know if it works!!

The GL_CLAMP helps, but changing the rest of the code doesn't solve the problem. I changed the texture filtering parameters and that solved it.

lol, ok, sorry about that.
I thought I was right because I had the exact same problem once and messing with
glAlphaFunc(GL_GREATER, 0);
solved it.

Quote:

Original post by RunningInt I am actually loading RGBA files from disk. I have no paint program that can create bitmaps with alpha channel so I made a program to convert an RGB bitmap file into a raw ARGB data file using a key color.

To clarify, bmps do not support alpha channels. I would recommend using TGAs instead, as they maintain the image quality and support alpha. If you are looking for a good paint program, I use The Gimp for my textures and image conversion needs. It is free and pretty powerful. There is also a tutorial on nehe.gamedev.net that goes over tga loading (without using RLE compression, search these forums to find some code for that).

Hope this helps.

Quote:

Original post by RunningInt I had to use GL_CLAMP as I don't seem to have CLAMP_TO_EDGE defined. Is there a problem with GL_CLAMP?

CLAMP just clamps to the border colour (ie a single colour for the whole texture) and isn't the right way to go about it. CLAMP_TO_EDGE correctly limits the texture coords to not wrap around as you need. CLAMP_TO_EDGE was introduced in OpenGL 1.2, so it's not in the default 1.1 headers that come with Visual Studio. Check the forum faq for a good overview of using greater than 1.1.