Question

I am using OpenGL to draw textures in my game.

glClear(GL_COLOR_BUFFER_BIT);

float w = 128;
float h = 128;

w *= scale;
h *= scale;

GLfloat vertices[] = {
    w, 0,
    w, h,
    0, 0,
    0, h
};

float u1 = 0;
float u2 = 1;
float v1 = 0;
float v2 = 1;

GLfloat texCoords[] = {
    u2, v1,
    u2, v2,
    u1, v1,
    u1, v2
};

glVertexPointer(2, GL_FLOAT, 0, vertices);
glEnableClientState(GL_VERTEX_ARRAY);
glTexCoordPointer(2, GL_FLOAT, 0, texCoords);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);

glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

It is a simple example to explain my problem. I change scale variable, which impacts only on triangle vertices and should not alter texture coordinates. When scale is 1, i have this picture:

one http://dl.dropbox.com/u/21467/opengl/1.png

When I change scale to 0.99, I have this picture:

two http://dl.dropbox.com/u/21467/opengl/3.png

If you look carefully, you notice little stripe on the top of the texture. Why is it there and how can I avoid it?

In my real game I draw tiles and if I change scale, my tiles start having those stripes and in result I got this nasty grid of stripes in my game. Does anybody know, what is wrong?

Answer 1

Call the following code when creating the texture buffer:

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

If you look carefully, you notice little stripe on the top of the texture. Why is it there and how can I avoid it?

What is happening is that at certain pixels, the texture coordinate at that screen position may be something like -0.0001, or 1.0002. The TEXTURE_WRAP_[S/T] texture parameter details what will happen when this occurs.