using simple shaders I've found a way to create gradients.
It's nice, but I still need to display this gradient pattern on each face of my meshes. Or on the billboard face, just like it's a texture.
The glsl function gl_FragCoord returns window-related coordinates. Could someone explain me the way how to translate this into face-related coords and then draw my pattern?
Okey. A little surfing of stackoverflow gave me this topic: OpenGL: How to render perfect rectangular gradient?
Here is the meaning string: gl_FragColor = mix(color0, color1, uv.u + uv.v - 2 * uv.u * uv.v);
Of course we cannot translate window-space coordinates into something "face-related", but we could use UV coordinates of a face. So, I decided, what if we have a square face with uv-coordinates corresponding to full-sized texture (like 0,0; 0,1; 1,0; 1,1); So the center of a structure is 0.5,0.5. This could be a center of my round-gradient.
so my code of fragment shader is:
vec2 u_c = vec2(0.5,0.5);
float distanceFromLight = length(uv - u_c);
gl_FragColor = mix(vec4(1.,0.5,1.,1.), vec4(0.,0.,0.,1.), distanceFromLight*2.0);
Vertex shader:
gl_Position = _mvProj * vec4(vertex, 1.0);
uv = uv1;
Of course, we need to give correct UV coordinates, but the point is understood.