Android OpenGL Texture Mapping / Texture Atlas

Question

Good evening all

I am trying to get my OpenGL program to use 1 texture (texture Atlas). It is 256 x 256. I load it as a normal texture.

If the texture is from 0,0 to 1,1 then I believe each square is 0.2 in size.

The issue is only the 1st and 3rd texture work. The 2nd is odd and the 4th seems to be 2nd+3rd texture and 5th is the 2nd,3rd and 4th put together

So I built a simple function to return the texture coords

    int yy = textureId / 5;
    int xx = textureId % 5;
    float size = 1.0f / 5;

    float[] textureCoordinateDataMap = createTexture(size * xx,size * yy ,size, size );


    public float[]createTexture(float x, float y, float xx, float yy)
    {
         float[] textureCoordinateDataMap =
                 {
                         // Front face
                         x, y,
                         x, yy,
                         xx, y,
                         x, yy,
                         xx, yy,
                         xx, y,

                         // Right face
                         x, y,
                         x, yy,
                         xx, y,
                         x, yy,
                         xx, yy,
                         xx, y,

                         // Back face
                         x, y,
                         x, yy,
                         xx, y,
                         x, yy,
                         xx, yy,
                         xx, y,

                         // Left face
                         x, y,
                         x, yy,
                         xx, y,
                         x, yy,
                         xx, yy,
                         xx, y,

                         // Top face
                         x, y,
                         x, yy,
                         xx, y,
                         x, yy,
                         xx, yy,
                         xx, y,

                         // Bottom face
                         x, y,
                         x, yy,
                         xx, y,
                         x, yy,
                         xx, yy,
                         xx, y,
                 };

        return textureCoordinateDataMap;
    }

I have tried to hardcode the values, the only ones that work are 0,0 0.4,0 0,0.4 0.4,0.4

Answer 1

If you want to use the values in this array as texture coordinates, you will need to add the size to the left/lower coordinate to get the right/top coordinate. Right now you use the size itself as the right/top coordinate. One way is to add the size in the function call:

float[] textureCoordinateDataMap = createTexture(
     size * xx, size * yy , size (xx + 1), size * (yy + 1));