vulkan: Handle generating mipmaps for 1x1 images

Testcase included.

gsk/gpu/gskgpurenderpassop.c

@@ -245,7 +245,9 @@ gsk_gpu_render_pass_end_op_vk_command (GskGpuOp              *op,
 
   vkCmdEndRenderPass (state->vk_command_buffer);
 
-  if (gsk_gpu_image_get_flags (self->target) & GSK_GPU_IMAGE_CAN_MIPMAP)
+  if ((gsk_gpu_image_get_flags (self->target) & GSK_GPU_IMAGE_CAN_MIPMAP) &&
+      (gsk_gpu_image_get_width (self->target) > 1 ||
+       gsk_gpu_image_get_height (self->target) > 1))
     {
       vkCmdPipelineBarrier (state->vk_command_buffer,
                             gsk_vulkan_image_get_vk_pipeline_stage (GSK_VULKAN_IMAGE (self->target)),

gsk/gpu/gskvulkanimageprivate.h

@@ -71,7 +71,7 @@ static inline guint
 gsk_vulkan_mipmap_levels (gsize width,
                           gsize height)
 {
-  return g_bit_nth_msf (MAX (width, height) - 1, -1) + 1;
+  return g_bit_nth_msf (MAX (MAX (width, height) - 1, 1), -1) + 1;
 }
 
 G_END_DECLS

testsuite/gsk/compare/mipmap-with-1x1.node

@@ -0,0 +1,7 @@
+texture-scale {
+  bounds: 0 0 10 10;
+  filter: trilinear;
+  texture: url("data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVQImWP4z8DwHwAFAAH/q842\
+iQAAAABJRU5ErkJggg==\
+");
+}

testsuite/gsk/meson.build

@@ -104,6 +104,7 @@ compare_render_tests = [
   'mask-modes-with-alpha',
   'mask-texture-color-alpha',
   'mipmap-generation-later',
+  'mipmap-with-1x1',
   'nested-rounded-clips',
   'offscreen-forced-downscale',
   'offscreen-fractional-translate-nogl',