non uniform scale and then rotation creates squashed sprite.

OpenGL OpenGL: Basic Coding
1

I am drawing a sprite and when it’s a square and I rotate it, there’s no problem. When I do a non uniform scale such as stretch the height 2x the width then rotate. The sprite will seem to get squished when it is rotated.

I am using the vectormath library; this is rotation code with all the intermediate functions also documented


static inline void vmathM4MakeRotationZ( VmathMatrix4 *result, float radians )
{
    float s, c;
    s = sinf( radians );
    c = cosf( radians );
    vmathV4MakeFromElems( &result->col0, c, s, 0.0f, 0.0f );
    vmathV4MakeFromElems( &result->col1, -s, c, 0.0f, 0.0f );
    vmathV4MakeZAxis( &result->col2 );
    vmathV4MakeWAxis( &result->col3 );
}

static inline void vmathV4MakeFromElems(VmathVector4 *result, float _x,
                                        float _y, float _z, float _w) {
    result->x = _x;
    result->y = _y;
    result->z = _z;
    result->w = _w;
}

static inline void vmathV4MakeZAxis(VmathVector4 *result) {
    vmathV4MakeFromElems(result, 0.0f, 0.0f, 1.0f, 0.0f);
}

Why does a non uniform scale cause such an issue and how can I solve it?

2

If you’re trying to scale the sprite, the matrices should be multiplied with the rotation on the left and the scale on the right.

3

changing the multiplication order for my scale and rotation it now rotates properly but if I translate after rotating it seems to offset the origin of the quad.