Transparency Sorting - OpenGL Wiki

Blending can be used to make objects appear transparent. However, blending alone is not enough. There are a number of steps that you must take to make transparency work. When you draw things with blending turned on, the renderer reads back pixels from the frame buffer, mixes in the new color and puts the pixels back where they came from. In many cases, transparency is a binary decision. The texels of a texture mapped to the polygon causes parts of it to be completely opaque, and other parts to be completely transparent. The texture's alpha values are used to make "cutout" objects. If you want to draw something complicated like a tree, you probably can't afford a polygon for every single leaf and branch; so you use an texture that has pictures of leaves. In this case, the leaf texture has no translucent texels; either the texel is opaque or it is completely transparent. Texels that are opaque have an alpha of 1.0, and texels that are transparent have an alpha of 0.0. If this is your cas

Blending can be used to make objects appear transparent. However, blending alone is not enough. There are a number of steps that you must take to make transparency work. When you draw things with blending turned on, the renderer reads back pixels from the frame buffer, mixes in the new color and puts the pixels back where they came from. In many cases, transparency is a binary decision. The texels of a texture mapped to the polygon causes parts of it to be completely opaque, and other parts to be completely transparent. The texture's alpha values are used to make "cutout" objects. If you want