OpenGL texture format enums table

For reference, here are the OpenGL texture formats/internal formats enums corresponding to each compressed texture format in the transcoder_texture_format enum in transcoder/basisu_transcoder.h. The command line tool uses these OpenGL enums when it writes .KTX format texture files.

transcoder_texture_format	GL internal format	GL base internal format
cTFBC1_RGB	GL_COMPRESSED_RGB_S3TC_DXT1_EXT	GL_RGB
cTFBC3_RGBA	GL_COMPRESSED_RGBA_S3TC_DXT5_EXT	GL_RGBA
cTFBC4_R	GL_COMPRESSED_RED_RGTC1_EXT	GL_RED
cTFBC5_RG	GL_COMPRESSED_RED_GREEN_RGTC2_EXT	GL_RG
cTFETC1_RGB	GL_ETC1_RGB8_OES	GL_RGB
cTFETC2_RGBA	GL_COMPRESSED_RGBA8_ETC2_EAC	GL_RGBA
cTFBC7_M6_RGB, cTFBC7_M5_RGBA	GL_COMPRESSED_RGBA_BPTC_UNORM	GL_RGBA
cTFPVRTC1_4_RGB	GL_COMPRESSED_RGB_PVRTC_4BPPV1_IMG	GL_RGB
cTFPVRTC1_4_RGBA	GL_COMPRESSED_RGBA_PVRTC_4BPPV1_IMG	GL_RGBA
cTFASTC_4x4_RGBA	GL_COMPRESSED_RGBA_ASTC_4x4_KHR	GL_RGBA
cTFATC_RGB	GL_ATC_RGB_AMD	GL_RGB
cTFATC_RGBA	GL_ATC_RGBA_INTERPOLATED_ALPHA_AMD	GL_RGBA
cTFETC2_EAC_R11	GL_COMPRESSED_R11_EAC	GL_RED
cTFETC2_EAC_RG11	GL_COMPRESSED_RG11_EAC	GL_RG
cTFFXT1_RGB	GL_COMPRESSED_RGB_FXT1_3DFX	GL_RGB
cTFPVRTC2_4_RGB, cTFPVRTC2_4_RGBA	GL_COMPRESSED_RGBA_PVRTC_4BPPV2_IMG	GL_RGBA