Interpolate Texture in TextureAtlas - opengl

Question

I'm searching for a way to interpolate / smooth a texture which is red from a texture atlas.
That problem is that if i set the MIN_FILTER to GL_LINEAR i'll get bleeding at the edges. (the pixel of the next texture are used for interpolation)
I tried solving this by writing a shader which does the interpolation manually but to detect which pixels it has to ignore, the shader has to know the texCoords of the vertices so that it can calculate if the pixel used is in or outside of the triangle. To get the texCoords into the shader i tried to use uniform but i use DisplayLists (i considered switching to VBOs, but my first implemetation used them and it was extremly slow) which makes it very complicated.
How can i smooth my textures without bleeding?
Another problem is that the method that checks if a point is in a triangle doesn't seem to work.
Vertex Shader:
#version 130
void main()
{
gl_TexCoord[0] = gl_TextureMatrix[0] * gl_MultiTexCoord0;
gl_FrontColor = gl_Color;
gl_Position = ftransform();
}
Fragement Shader:
#version 130
uniform sampler2D tex;
uniform vec2 texCoord[4];
float textureSize;
float texelSize;
bool pointInTriangle(vec3 P, vec3 A, vec3 B, vec3 C)
{
vec3 u = B - A;
vec3 v = C - A;
vec3 w = P - A;
vec3 vCrossW = cross(v, w);
vec3 vCrossU = cross(v, u);
if(dot(vCrossW, vCrossU) < 0)
{
return false;
}
vec3 uCrossW = cross(u, w);
vec3 uCrossV = cross(u, v);
if(dot(uCrossW, uCrossV) < 0)
{
return false;
}
float denom = length(uCrossV);
float r = length(vCrossW);
float t = length(uCrossW);
return (r + t <= 1);
}
vec4 texture2DBilinear(sampler2D textureSampler, vec2 uv)
{
vec4 tl = texture2D(textureSampler, uv);
vec4 tr = texture2D(textureSampler, uv + vec2(texelSize, 0));
vec4 bl = texture2D(textureSampler, uv + vec2(0, texelSize));
vec4 br = texture2D(textureSampler, uv + vec2(texelSize , texelSize));
vec2 f = fract( uv.xy * textureSize );
vec4 tA = mix( tl, tr, f.x );
vec4 tB = mix( bl, br, f.x );
return mix( tA, tB, f.y );
}
void main()
{
ivec2 textureSize2d = textureSize(tex,0);
textureSize = float(textureSize2d.x);
texelSize = 1.0 / textureSize;
//texture coordinate:
vec2 texCoord = (gl_TexCoord[0].st);
//vec4 color = texture2D(tex,gl_TexCoord[0].st);
gl_FragColor = texture2DBilinear(tex, texCoord) * gl_Color;
//TEST IF METHOD WORKS
if(pointInTriangle(vec3(1,1,0),vec3(0,0,0),vec3(3,0,0),vec3(0,3,0)))
{
//pointInTriangle DOES NOT WORK!
gl_FragColor = gl_Color;
}
}