About the texture switch in OpenGLES

Question

When the texture is switched, why is the speed slow?

---

Code - 1

 glBindTexture(GL_TEXTURE_2D,texId01);

 glDrawArray(glDrawArrays(GL_TRIANGLES, 0, 4);

 glBindTexture(GL_TEXTURE_2D,texId02);

 glDrawArray(glDrawArrays(GL_TRIANGLES, 0, 4);

---

Code - 2

 glBindTexture(GL_TEXTURE_2D,texId01);

 glDrawArray(GL_TRIANGLES, 0, 4);

 glDrawArray(GL_TRIANGLES, 0, 4);

---

Why are these speeds different?

Answer 1

Because the driver must do some internal validations, to check that everything is as expected, so binding a texture is a expensive operation.

With that in mind, you should minimize texture binding operations. A common way of doing it is sort primitives by texture (and shader also, if GL ES 2.0) when drawing.