func (c *drawImageCommand) Exec(context *opengl.Context, indexOffsetInBytes int) error {
f, err := c.dst.createFramebufferIfNeeded(context)
if err != nil {
return err
}
if err := f.setAsViewport(context); err != nil {
return err
}
context.BlendFunc(c.mode)
n := c.quadsNum()
if n == 0 {
return nil
}
_, h := c.dst.Size()
proj := f.projectionMatrix(h)
p := &programContext{
state: &theOpenGLState,
program: theOpenGLState.programTexture,
context: context,
projectionMatrix: proj,
texture: c.src.texture.native,
colorM: c.color,
}
if err := p.begin(); err != nil {
return err
}
// TODO: We should call glBindBuffer here?
// The buffer is already bound at begin() but it is counterintuitive.
context.DrawElements(opengl.Triangles, 6*n, indexOffsetInBytes)
return nil
}