[vulkan] Add an undefined to shader-ro barrier

I guess it's kind of UB, but it's handy for images that will be
conditionally written by the GPU but need to be in shader-read-only for
draw calls and the validation layers can't tell that the layers won't be
used.

include/QF/Vulkan/barrier.h

@@ -22,6 +22,7 @@ typedef struct qfv_bufferbarrier_s {
 enum {
 	qfv_LT_Undefined_to_TransferDst,
 	qfv_LT_Undefined_to_General,
+	qfv_LT_Undefined_to_ShaderReadOnly,
 	qfv_LT_TransferDst_to_TransferSrc,
 	qfv_LT_TransferDst_to_General,
 	qfv_LT_TransferDst_to_ShaderReadOnly,

libs/video/renderer/vulkan/barrier.c

@@ -57,6 +57,19 @@ const qfv_imagebarrier_t imageBarriers[] = {
 			{ VK_IMAGE_ASPECT_COLOR_BIT, 0, 1, 0, 1 }
 		},
 	},
+	[qfv_LT_Undefined_to_ShaderReadOnly] = {
+		.srcStages = VK_PIPELINE_STAGE_TOP_OF_PIPE_BIT,
+		.dstStages = VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT,
+		.barrier = {
+			VK_STRUCTURE_TYPE_IMAGE_MEMORY_BARRIER, 0,
+			0,
+			VK_ACCESS_SHADER_READ_BIT,
+			VK_IMAGE_LAYOUT_UNDEFINED,
+			VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL,
+			VK_QUEUE_FAMILY_IGNORED, VK_QUEUE_FAMILY_IGNORED, 0,
+			{ VK_IMAGE_ASPECT_COLOR_BIT, 0, 1, 0, 1 }
+		},
+	},
 	[qfv_LT_TransferDst_to_TransferSrc] = {
 		.srcStages = VK_PIPELINE_STAGE_TRANSFER_BIT,
 		.dstStages = VK_PIPELINE_STAGE_TRANSFER_BIT,