Support running on the "low power" GPU on dual GPU macOS machines

Fixes #136

CHANGELOG.rst

@@ -24,6 +24,8 @@ version 0.6.0 [future]
 
 - Use CoreText instead of FreeType to render text on macOS
 
+- Support running on the "low power" GPU on dual GPU macOS machines
+
 - Add a new "grid" window layout
 
 - Drop the dependency on glfw (kitty now uses a modified, bundled copy of glfw)

kitty/glfw.c

@@ -227,6 +227,7 @@ create_os_window(PyObject UNUSED *self, PyObject *args) {
         glfwWindowHint(GLFW_STENCIL_BITS, 0);
 #ifdef __APPLE__
         if (OPT(macos_hide_titlebar)) glfwWindowHint(GLFW_DECORATED, false);
+        glfwWindowHint(GLFW_COCOA_GRAPHICS_SWITCHING, true);
 #endif
 
         standard_cursor = glfwCreateStandardCursor(GLFW_IBEAM_CURSOR);

kitty/shaders.c

@@ -114,6 +114,12 @@ layout_sprite_map() {
     if (!limits_updated) {
         glGetIntegerv(GL_MAX_TEXTURE_SIZE, &(sprite_map.max_texture_size)); 
         glGetIntegerv(GL_MAX_ARRAY_TEXTURE_LAYERS, &(sprite_map.max_array_texture_layers)); 
+#ifdef __APPLE__
+        // Since on Apple we could have multiple GPUs, with different capabilities,
+        // upper bound the values according to the data from http://developer.apple.com/graphicsimaging/opengl/capabilities/
+        sprite_map.max_texture_size = MIN(8192, sprite_map.max_texture_size);
+        sprite_map.max_array_texture_layers = MIN(512, sprite_map.max_array_texture_layers);
+#endif
         sprite_tracker_set_limits(sprite_map.max_texture_size, sprite_map.max_array_texture_layers);
         limits_updated = true;
     }