enable alpha blending

src/modules/graphics/vulkan/Graphics.cpp

@@ -1254,7 +1254,13 @@ namespace love {
 
 				VkPipelineColorBlendAttachmentState colorBlendAttachment{};
 				colorBlendAttachment.colorWriteMask = VK_COLOR_COMPONENT_R_BIT | VK_COLOR_COMPONENT_G_BIT | VK_COLOR_COMPONENT_B_BIT | VK_COLOR_COMPONENT_A_BIT;
-				colorBlendAttachment.blendEnable = VK_FALSE;
+				colorBlendAttachment.blendEnable = VK_TRUE;
+				colorBlendAttachment.srcColorBlendFactor = VK_BLEND_FACTOR_SRC_ALPHA;
+				colorBlendAttachment.dstColorBlendFactor = VK_BLEND_FACTOR_ONE_MINUS_SRC_ALPHA;
+				colorBlendAttachment.colorBlendOp = VK_BLEND_OP_ADD;
+				colorBlendAttachment.srcAlphaBlendFactor = VK_BLEND_FACTOR_ONE;
+				colorBlendAttachment.dstAlphaBlendFactor = VK_BLEND_FACTOR_ZERO;
+				colorBlendAttachment.alphaBlendOp = VK_BLEND_OP_ADD;
 
 				VkPipelineColorBlendStateCreateInfo colorBlending{};
 				colorBlending.sType = VK_STRUCTURE_TYPE_PIPELINE_COLOR_BLEND_STATE_CREATE_INFO;