From 2ee55ac3adae04d8a773a16220dc8f657f093ed8 Mon Sep 17 00:00:00 2001
From: Amber <amber@igalia.com>
Date: Wed, 26 Oct 2022 14:06:15 +0200
Subject: [PATCH] Use index buffers.

---
 src/main.c | 43 +++++++++++++++++++++++++++++++++++++++----
 1 file changed, 39 insertions(+), 4 deletions(-)

diff --git a/src/main.c b/src/main.c
index 5745a1e..d46cea0 100644
--- a/src/main.c
+++ b/src/main.c
@@ -73,6 +73,9 @@ typedef struct ApplicationState {
 
     VkBuffer vertex_buffer;
     VkDeviceMemory vertex_buffer_memory;
+
+    VkBuffer index_buffer;
+    VkDeviceMemory index_buffer_memory;
 } ApplicationState;
 
 typedef struct QueueFamilyIndices {
@@ -88,9 +91,14 @@ typedef struct Vertex {
 } Vertex;
 
 const Vertex vertices[] = {
-    {{0.0f, -0.5f}, {1.0f, 0.0f, 0.0f}},
-    {{0.5f,  0.5f}, {0.0f, 1.0f, 0.0f}},
-    {{-0.5f, 0.5f}, {0.0f, 0.0f, 1.0f}}
+    {{-0.5f, -0.5f}, {1.0f, 0.0f, 0.0f}},
+    {{0.5f, -0.5f},  {0.0f, 1.0f, 0.0f}},
+    {{0.5f, 0.5f},   {0.0f, 0.0f, 1.0f}},
+    {{-0.5f, 0.5f},  {1.0f, 1.0f, 1.0f}}
+};
+
+const uint16_t indices[] = {
+    0, 1, 2, 2, 3, 0
 };
 
 void create_window(ApplicationState* state) {
@@ -999,6 +1007,29 @@ void create_vertex_buffer(ApplicationState* state) {
     vkFreeMemory(state->device, staging_buffer_memory, NULL);
 }
 
+void create_index_buffer(ApplicationState* state) {
+    VkDeviceSize buffer_size = sizeof(uint16_t) * ARRSIZE(indices);
+
+    //we use a staging buffer for transferring data in order to use a more efficient memory type for the index buffer
+    VkBuffer staging_buffer;
+    VkDeviceMemory staging_buffer_memory;
+    create_buffer(state, buffer_size, VK_BUFFER_USAGE_TRANSFER_SRC_BIT, VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT | VK_MEMORY_PROPERTY_HOST_COHERENT_BIT,
+            &staging_buffer, &staging_buffer_memory);
+
+    void* data;
+    vkMapMemory(state->device, staging_buffer_memory, 0, buffer_size, 0, &data);
+    memcpy(data, indices, buffer_size);
+    vkUnmapMemory(state->device, staging_buffer_memory);
+
+    create_buffer(state, buffer_size, VK_BUFFER_USAGE_TRANSFER_DST_BIT | VK_BUFFER_USAGE_INDEX_BUFFER_BIT, VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT,
+            &state->index_buffer, &state->index_buffer_memory);
+
+    copy_buffer(state, staging_buffer, state->index_buffer, buffer_size);
+
+    vkDestroyBuffer(state->device, staging_buffer, NULL);
+    vkFreeMemory(state->device, staging_buffer_memory, NULL);
+}
+
 void create_command_buffer(ApplicationState* state) {
     VkCommandBufferAllocateInfo command_buf_allocate_info = {0};
     command_buf_allocate_info.sType = VK_STRUCTURE_TYPE_COMMAND_BUFFER_ALLOCATE_INFO;
@@ -1049,6 +1080,7 @@ void record_command_buffer(ApplicationState* state, VkCommandBuffer command_buff
     VkBuffer vertex_buffers[] = {state->vertex_buffer};
     VkDeviceSize offsets[] = {0};
     vkCmdBindVertexBuffers(command_buffer, 0, 1, vertex_buffers, offsets);
+    vkCmdBindIndexBuffer(command_buffer, state->index_buffer, 0, VK_INDEX_TYPE_UINT16);
 
     //setup dynamic state
     VkViewport viewport = {0};
@@ -1069,7 +1101,7 @@ void record_command_buffer(ApplicationState* state, VkCommandBuffer command_buff
     vkCmdSetScissor(command_buffer, 0, 1, &scissor);
 
     //vertex count, instance count, first vertex and first instance
-    vkCmdDraw(command_buffer, ARRSIZE(vertices), 1, 0, 0);
+    vkCmdDrawIndexed(command_buffer, ARRSIZE(indices), 1, 0, 0, 0);
 
     vkCmdEndRenderPass(command_buffer);
 
@@ -1112,6 +1144,7 @@ void init_vulkan(ApplicationState* state) {
     create_framebuffers(state);
     create_command_pool(state);
     create_vertex_buffer(state);
+    create_index_buffer(state);
     create_command_buffer(state);
     create_sync_objects(state);
 }
@@ -1194,6 +1227,8 @@ void terminate(ApplicationState* state) {
     }
     vkDestroyBuffer(state->device, state->vertex_buffer, NULL);
     vkFreeMemory(state->device, state->vertex_buffer_memory, NULL);
+    vkDestroyBuffer(state->device, state->index_buffer, NULL);
+    vkFreeMemory(state->device, state->index_buffer_memory, NULL);
 
     vkDestroySwapchainKHR(state->device, state->swapchain, NULL);
     vkDestroyDevice(state->device, NULL);