Seam issue when mapping a texture to a sphere in OpenGL

Question

I\'m trying to create geometry to represent the Earth in OpenGL. I have what\'s more or less a sphere (closer to the elliptical geoid that Earth is though). I map a texture

Answer 1

You can also go a dirty way: interpolate X,Y positions in between vertex shader and fragment shader and recalculate correct texture coordinate in fragment shader. This may be somewhat slower, but it doesn't involve duplicate vertexes and it's simplier, I think.

For example:
vertex shader:

#version 150 core
uniform mat4 projM;
uniform mat4 viewM;
uniform mat4 modelM;
in vec4 in_Position;
in vec2 in_TextureCoord;
out vec2 pass_TextureCoord;
out vec2 pass_xy_position;
void main(void) {
    gl_Position = projM * viewM * modelM * in_Position;
    pass_xy_position = in_Position.xy; // 2d spinning interpolates good!
    pass_TextureCoord = in_TextureCoord;
}

fragment shader:

#version 150 core
uniform sampler2D texture1;
in vec2 pass_xy_position;
in vec2 pass_TextureCoord;
out vec4 out_Color;

#define PI 3.141592653589793238462643383279

void main(void) {
    vec2 tc = pass_TextureCoord;
    tc.x = (PI + atan(pass_xy_position.y, pass_xy_position.x)) / (2 * PI); // calculate angle and map it to 0..1
    out_Color = texture(texture1, tc);
}