1GL_ARB_texture_env_combine
2https://www.khronos.org/registry/OpenGL/extensions/ARB/ARB_texture_env_combine.txt
3GL_ARB_texture_env_combine
4
5	GL_SUBTRACT_ARB 0x84E7
6	GL_COMBINE_ARB 0x8570
7	GL_COMBINE_RGB_ARB 0x8571
8	GL_COMBINE_ALPHA_ARB 0x8572
9	GL_RGB_SCALE_ARB 0x8573
10	GL_ADD_SIGNED_ARB 0x8574
11	GL_INTERPOLATE_ARB 0x8575
12	GL_CONSTANT_ARB 0x8576
13	GL_PRIMARY_COLOR_ARB 0x8577
14	GL_PREVIOUS_ARB 0x8578
15	GL_SOURCE0_RGB_ARB 0x8580
16	GL_SOURCE1_RGB_ARB 0x8581
17	GL_SOURCE2_RGB_ARB 0x8582
18	GL_SOURCE0_ALPHA_ARB 0x8588
19	GL_SOURCE1_ALPHA_ARB 0x8589
20	GL_SOURCE2_ALPHA_ARB 0x858A
21	GL_OPERAND0_RGB_ARB 0x8590
22	GL_OPERAND1_RGB_ARB 0x8591
23	GL_OPERAND2_RGB_ARB 0x8592
24	GL_OPERAND0_ALPHA_ARB 0x8598
25	GL_OPERAND1_ALPHA_ARB 0x8599
26	GL_OPERAND2_ALPHA_ARB 0x859A
27