1GL_ARB_texture_env_combine
2http://www.opengl.org/registry/specs/ARB/texture_env_combine.txt
3GL_ARB_texture_env_combine
4	GL_SUBTRACT_ARB 0x84E7
5	GL_COMBINE_ARB 0x8570
6	GL_COMBINE_RGB_ARB 0x8571
7	GL_COMBINE_ALPHA_ARB 0x8572
8	GL_RGB_SCALE_ARB 0x8573
9	GL_ADD_SIGNED_ARB 0x8574
10	GL_INTERPOLATE_ARB 0x8575
11	GL_CONSTANT_ARB 0x8576
12	GL_PRIMARY_COLOR_ARB 0x8577
13	GL_PREVIOUS_ARB 0x8578
14	GL_SOURCE0_RGB_ARB 0x8580
15	GL_SOURCE1_RGB_ARB 0x8581
16	GL_SOURCE2_RGB_ARB 0x8582
17	GL_SOURCE0_ALPHA_ARB 0x8588
18	GL_SOURCE1_ALPHA_ARB 0x8589
19	GL_SOURCE2_ALPHA_ARB 0x858A
20	GL_OPERAND0_RGB_ARB 0x8590
21	GL_OPERAND1_RGB_ARB 0x8591
22	GL_OPERAND2_RGB_ARB 0x8592
23	GL_OPERAND0_ALPHA_ARB 0x8598
24	GL_OPERAND1_ALPHA_ARB 0x8599
25	GL_OPERAND2_ALPHA_ARB 0x859A
26