Fix build for OpenGL 2.1, where half floats are part of an extension (#3233)

src/rlgl.h

@@ -3267,11 +3267,17 @@ void rlGetGlTextureFormats(int format, unsigned int *glInternalFormat, unsigned
         case RL_PIXELFORMAT_UNCOMPRESSED_R32: if (RLGL.ExtSupported.texFloat32) *glInternalFormat = GL_LUMINANCE; *glFormat = GL_LUMINANCE; *glType = GL_FLOAT; break;            // NOTE: Requires extension OES_texture_float
         case RL_PIXELFORMAT_UNCOMPRESSED_R32G32B32: if (RLGL.ExtSupported.texFloat32) *glInternalFormat = GL_RGB; *glFormat = GL_RGB; *glType = GL_FLOAT; break;                  // NOTE: Requires extension OES_texture_float
         case RL_PIXELFORMAT_UNCOMPRESSED_R32G32B32A32: if (RLGL.ExtSupported.texFloat32) *glInternalFormat = GL_RGBA; *glFormat = GL_RGBA; *glType = GL_FLOAT; break;             // NOTE: Requires extension OES_texture_float
+        #if defined(GRAPHICS_API_OPENGL_21)
+        case RL_PIXELFORMAT_UNCOMPRESSED_R16: if (RLGL.ExtSupported.texFloat16) *glInternalFormat = GL_LUMINANCE; *glFormat = GL_LUMINANCE; *glType = GL_HALF_FLOAT_ARB; break;
+        case RL_PIXELFORMAT_UNCOMPRESSED_R16G16B16: if (RLGL.ExtSupported.texFloat16) *glInternalFormat = GL_RGB; *glFormat = GL_RGB; *glType = GL_HALF_FLOAT_ARB; break;
+        case RL_PIXELFORMAT_UNCOMPRESSED_R16G16B16A16: if (RLGL.ExtSupported.texFloat16) *glInternalFormat = GL_RGBA; *glFormat = GL_RGBA; *glType = GL_HALF_FLOAT_ARB; break;
+        #else // defined(GRAPHICS_API_OPENGL_ES2)
         case RL_PIXELFORMAT_UNCOMPRESSED_R16: if (RLGL.ExtSupported.texFloat16) *glInternalFormat = GL_LUMINANCE; *glFormat = GL_LUMINANCE; *glType = GL_HALF_FLOAT_OES; break;   // NOTE: Requires extension OES_texture_half_float
         case RL_PIXELFORMAT_UNCOMPRESSED_R16G16B16: if (RLGL.ExtSupported.texFloat16) *glInternalFormat = GL_RGB; *glFormat = GL_RGB; *glType = GL_HALF_FLOAT_OES; break;         // NOTE: Requires extension OES_texture_half_float
         case RL_PIXELFORMAT_UNCOMPRESSED_R16G16B16A16: if (RLGL.ExtSupported.texFloat16) *glInternalFormat = GL_RGBA; *glFormat = GL_RGBA; *glType = GL_HALF_FLOAT_OES; break;    // NOTE: Requires extension OES_texture_half_float
         #endif
         #endif
+        #endif
     #elif defined(GRAPHICS_API_OPENGL_33)
         case RL_PIXELFORMAT_UNCOMPRESSED_GRAYSCALE: *glInternalFormat = GL_R8; *glFormat = GL_RED; *glType = GL_UNSIGNED_BYTE; break;
         case RL_PIXELFORMAT_UNCOMPRESSED_GRAY_ALPHA: *glInternalFormat = GL_RG8; *glFormat = GL_RG; *glType = GL_UNSIGNED_BYTE; break;