20_index_buffer.diff

diff --git a/../steps/19_staging_buffer/main.go b/../steps/20_index_buffer/main.go
index ddb8bcf..9fbfac7 100644
--- a/../steps/19_staging_buffer/main.go
+++ b/../steps/20_index_buffer/main.go
@@ -80,11 +80,14 @@ func getVertexAttributeDescriptions() []core1_0.VertexInputAttributeDescription
 }
 
 var vertices = []Vertex{
-	{X: 0, Y: -0.5, R: 1, G: 0, B: 0},
-	{X: 0.5, Y: 0.5, R: 0, G: 1, B: 0},
-	{X: -0.5, Y: 0.5, R: 0, G: 0, B: 1},
+	{X: -0.5, Y: -0.5, R: 1, G: 0, B: 0},
+	{X: 0.5, Y: -0.5, R: 0, G: 1, B: 0},
+	{X: 0.5, Y: 0.5, R: 0, G: 0, B: 1},
+	{X: -0.5, Y: 0.5, R: 1, G: 1, B: 1},
 }
 
+var indices = []uint16{0, 1, 2, 2, 3, 0}
+
 type HelloTriangleApplication struct {
 	globalDriver     core1_0.GlobalDriver
 	instanceDriver   core1_0.CoreInstanceDriver
@@ -123,6 +126,8 @@ type HelloTriangleApplication struct {
 
 	vertexBuffer       core1_0.Buffer
 	vertexBufferMemory core1_0.DeviceMemory
+	indexBuffer        core1_0.Buffer
+	indexBufferMemory  core1_0.DeviceMemory
 }
 
 func (app *HelloTriangleApplication) Run() error {
@@ -220,6 +225,11 @@ func (app *HelloTriangleApplication) initVulkan() error {
 		return err
 	}
 
+	err = app.createIndexBuffer()
+	if err != nil {
+		return err
+	}
+
 	err = app.createCommandBuffers()
 	if err != nil {
 		return err
@@ -309,6 +319,14 @@ func (app *HelloTriangleApplication) cleanupSwapChain() {
 func (app *HelloTriangleApplication) cleanup() {
 	app.cleanupSwapChain()
 
+	if app.indexBuffer.Initialized() {
+		app.deviceDriver.DestroyBuffer(app.indexBuffer, nil)
+	}
+
+	if app.indexBufferMemory.Initialized() {
+		app.deviceDriver.FreeMemory(app.indexBufferMemory, nil)
+	}
+
 	if app.vertexBuffer.Initialized() {
 		app.deviceDriver.DestroyBuffer(app.vertexBuffer, nil)
 	}
@@ -952,6 +970,34 @@ func (app *HelloTriangleApplication) createVertexBuffer() error {
 	return app.copyBuffer(stagingBuffer, app.vertexBuffer, bufferSize)
 }
 
+func (app *HelloTriangleApplication) createIndexBuffer() error {
+	bufferSize := binary.Size(indices)
+
+	stagingBuffer, stagingBufferMemory, err := app.createBuffer(bufferSize, core1_0.BufferUsageTransferSrc, core1_0.MemoryPropertyHostVisible|core1_0.MemoryPropertyHostCoherent)
+	if stagingBuffer.Initialized() {
+		defer app.deviceDriver.DestroyBuffer(stagingBuffer, nil)
+	}
+	if stagingBufferMemory.Initialized() {
+		defer app.deviceDriver.FreeMemory(stagingBufferMemory, nil)
+	}
+
+	if err != nil {
+		return err
+	}
+
+	err = writeData(app.deviceDriver, stagingBufferMemory, 0, indices)
+	if err != nil {
+		return err
+	}
+
+	app.indexBuffer, app.indexBufferMemory, err = app.createBuffer(bufferSize, core1_0.BufferUsageTransferDst|core1_0.BufferUsageIndexBuffer, core1_0.MemoryPropertyDeviceLocal)
+	if err != nil {
+		return err
+	}
+
+	return app.copyBuffer(stagingBuffer, app.indexBuffer, bufferSize)
+}
+
 func (app *HelloTriangleApplication) createBuffer(size int, usage core1_0.BufferUsageFlags, properties core1_0.MemoryPropertyFlags) (core1_0.Buffer, core1_0.DeviceMemory, error) {
 	buffer, _, err := app.deviceDriver.CreateBuffer(nil, core1_0.BufferCreateInfo{
 		Size:        size,
@@ -1076,7 +1122,8 @@ func (app *HelloTriangleApplication) createCommandBuffers() error {
 
 		app.deviceDriver.CmdBindPipeline(buffer, core1_0.PipelineBindPointGraphics, app.graphicsPipeline)
 		app.deviceDriver.CmdBindVertexBuffers(buffer, 0, []core1_0.Buffer{app.vertexBuffer}, []int{0})
-		app.deviceDriver.CmdDraw(buffer, 3, 1, 0, 0)
+		app.deviceDriver.CmdBindIndexBuffer(buffer, app.indexBuffer, 0, core1_0.IndexTypeUInt16)
+		app.deviceDriver.CmdDrawIndexed(buffer, len(indices), 1, 0, 0, 0)
 		app.deviceDriver.CmdEndRenderPass(buffer)
 
 		_, err = app.deviceDriver.EndCommandBuffer(buffer)