// Copyright 2018 The Ebiten Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// +build darwin

package metal

import (
	"fmt"
	"strings"
	"unsafe"

	"github.com/hajimehoshi/ebiten/v2/internal/affine"
	"github.com/hajimehoshi/ebiten/v2/internal/driver"
	"github.com/hajimehoshi/ebiten/v2/internal/graphics"
	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver/metal/ca"
	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver/metal/mtl"
	"github.com/hajimehoshi/ebiten/v2/internal/shaderir"
)

// #cgo CFLAGS: -x objective-c
// #cgo !ios CFLAGS: -mmacosx-version-min=10.12
// #cgo LDFLAGS: -framework Foundation
//
// #import <Foundation/Foundation.h>
//
// static void* allocAutoreleasePool() {
//   return [[NSAutoreleasePool alloc] init];
// }
//
// static void releaseAutoreleasePool(void* pool) {
//   [(NSAutoreleasePool*)pool release];
// }
import "C"

const source = `#include <metal_stdlib>

#define FILTER_NEAREST {{.FilterNearest}}
#define FILTER_LINEAR {{.FilterLinear}}
#define FILTER_SCREEN {{.FilterScreen}}

#define ADDRESS_CLAMP_TO_ZERO {{.AddressClampToZero}}
#define ADDRESS_REPEAT {{.AddressRepeat}}
#define ADDRESS_UNSAFE {{.AddressUnsafe}}

using namespace metal;

struct VertexIn {
  packed_float2 position;
  packed_float2 tex;
  packed_float4 color;
};

struct VertexOut {
  float4 position [[position]];
  float2 tex;
  float4 color;
};

vertex VertexOut VertexShader(
  uint vid [[vertex_id]],
  const device VertexIn* vertices [[buffer(0)]],
  constant float2& viewport_size [[buffer(1)]]
) {
  float4x4 projectionMatrix = float4x4(
    float4(2.0 / viewport_size.x, 0, 0, 0),
    float4(0, 2.0 / viewport_size.y, 0, 0),
    float4(0, 0, 1, 0),
    float4(-1, -1, 0, 1)
  );

  VertexIn in = vertices[vid];
  VertexOut out = {
    .position = projectionMatrix * float4(in.position, 0, 1),
    .tex = in.tex,
    .color = in.color,
  };

  return out;
}

float FloorMod(float x, float y) {
  if (x < 0.0) {
    return y - (-x - y * floor(-x/y));
  }
  return x - y * floor(x/y);
}

template<uint8_t address>
float2 AdjustTexelByAddress(float2 p, float4 source_region);

template<>
inline float2 AdjustTexelByAddress<ADDRESS_CLAMP_TO_ZERO>(float2 p, float4 source_region) {
  return p;
}

template<>
inline float2 AdjustTexelByAddress<ADDRESS_REPEAT>(float2 p, float4 source_region) {
  float2 o = float2(source_region[0], source_region[1]);
  float2 size = float2(source_region[2] - source_region[0], source_region[3] - source_region[1]);
  return float2(FloorMod((p.x - o.x), size.x) + o.x, FloorMod((p.y - o.y), size.y) + o.y);
}

template<uint8_t filter, uint8_t address>
struct ColorFromTexel;

constexpr sampler texture_sampler{filter::nearest};

template<>
struct ColorFromTexel<FILTER_NEAREST, ADDRESS_UNSAFE> {
  inline float4 Do(VertexOut v, texture2d<float> texture, constant float2& source_size, float scale, constant float4& source_region) {
    float2 p = v.tex;
    return texture.sample(texture_sampler, p);
  }
};

template<uint8_t address>
struct ColorFromTexel<FILTER_NEAREST, address> {
  inline float4 Do(VertexOut v, texture2d<float> texture, constant float2& source_size, float scale, constant float4& source_region) {
    float2 p = AdjustTexelByAddress<address>(v.tex, source_region);
    if (source_region[0] <= p.x &&
        source_region[1] <= p.y &&
        p.x < source_region[2] &&
        p.y < source_region[3]) {
      return texture.sample(texture_sampler, p);
    }
    return 0.0;
  }
};

template<>
struct ColorFromTexel<FILTER_LINEAR, ADDRESS_UNSAFE> {
  inline float4 Do(VertexOut v, texture2d<float> texture, constant float2& source_size, float scale, constant float4& source_region) {
    const float2 texel_size = 1 / source_size;

    // Shift 1/512 [texel] to avoid the tie-breaking issue.
    // As all the vertex positions are aligned to 1/16 [pixel], this shiting should work in most cases.
    float2 p0 = v.tex - texel_size / 2.0 + (texel_size / 512.0);
    float2 p1 = v.tex + texel_size / 2.0 + (texel_size / 512.0);

    float4 c0 = texture.sample(texture_sampler, p0);
    float4 c1 = texture.sample(texture_sampler, float2(p1.x, p0.y));
    float4 c2 = texture.sample(texture_sampler, float2(p0.x, p1.y));
    float4 c3 = texture.sample(texture_sampler, p1);

    float2 rate = fract(p0 * source_size);
    return mix(mix(c0, c1, rate.x), mix(c2, c3, rate.x), rate.y);
  }
};

template<uint8_t address>
struct ColorFromTexel<FILTER_LINEAR, address> {
  inline float4 Do(VertexOut v, texture2d<float> texture, constant float2& source_size, float scale, constant float4& source_region) {
    const float2 texel_size = 1 / source_size;

    // Shift 1/512 [texel] to avoid the tie-breaking issue.
    // As all the vertex positions are aligned to 1/16 [pixel], this shiting should work in most cases.
    float2 p0 = v.tex - texel_size / 2.0 + (texel_size / 512.0);
    float2 p1 = v.tex + texel_size / 2.0 + (texel_size / 512.0);
    p0 = AdjustTexelByAddress<address>(p0, source_region);
    p1 = AdjustTexelByAddress<address>(p1, source_region);

    float4 c0 = texture.sample(texture_sampler, p0);
    float4 c1 = texture.sample(texture_sampler, float2(p1.x, p0.y));
    float4 c2 = texture.sample(texture_sampler, float2(p0.x, p1.y));
    float4 c3 = texture.sample(texture_sampler, p1);

    if (p0.x < source_region[0]) {
      c0 = 0;
      c2 = 0;
    }
    if (p0.y < source_region[1]) {
      c0 = 0;
      c1 = 0;
    }
    if (source_region[2] <= p1.x) {
      c1 = 0;
      c3 = 0;
    }
    if (source_region[3] <= p1.y) {
      c2 = 0;
      c3 = 0;
    }

    float2 rate = fract(p0 * source_size);
    return mix(mix(c0, c1, rate.x), mix(c2, c3, rate.x), rate.y);
  }
};

template<uint8_t address>
struct ColorFromTexel<FILTER_SCREEN, address> {
  inline float4 Do(VertexOut v, texture2d<float> texture, constant float2& source_size, float scale, constant float4& source_region) {
    const float2 texel_size = 1 / source_size;

    float2 p0 = v.tex - texel_size / 2.0 / scale + (texel_size / 512.0);
    float2 p1 = v.tex + texel_size / 2.0 / scale + (texel_size / 512.0);

    float4 c0 = texture.sample(texture_sampler, p0);
    float4 c1 = texture.sample(texture_sampler, float2(p1.x, p0.y));
    float4 c2 = texture.sample(texture_sampler, float2(p0.x, p1.y));
    float4 c3 = texture.sample(texture_sampler, p1);

    float2 rate_center = float2(1.0, 1.0) - texel_size / 2.0 / scale;
    float2 rate = clamp(((fract(p0 * source_size) - rate_center) * scale) + rate_center, 0.0, 1.0);
    return mix(mix(c0, c1, rate.x), mix(c2, c3, rate.x), rate.y);
  }
};

template<bool useColorM, uint8_t filter, uint8_t address>
struct FragmentShaderImpl {
  inline float4 Do(
      VertexOut v,
      texture2d<float> texture,
      constant float2& source_size,
      constant float4x4& color_matrix_body,
      constant float4& color_matrix_translation,
      constant float& scale,
      constant float4& source_region) {
    float4 c = ColorFromTexel<filter, address>().Do(v, texture, source_size, scale, source_region);
    if (useColorM) {
      c.rgb /= c.a + (1.0 - sign(c.a));
      c = (color_matrix_body * c) + color_matrix_translation;
      c *= v.color;
      c.rgb *= c.a;
    } else {
      float4 s = v.color;
      c *= float4(s.r, s.g, s.b, 1.0) * s.a;
    }
    c = min(c, c.a);
    return c;
  }
};

template<bool useColorM, uint8_t address>
struct FragmentShaderImpl<useColorM, FILTER_SCREEN, address> {
  inline float4 Do(
      VertexOut v,
      texture2d<float> texture,
      constant float2& source_size,
      constant float4x4& color_matrix_body,
      constant float4& color_matrix_translation,
      constant float& scale,
      constant float4& source_region) {
    return ColorFromTexel<FILTER_SCREEN, address>().Do(v, texture, source_size, scale, source_region);
  }
};

// Define Foo and FooCp macros to force macro replacement.
// See "6.10.3.1 Argument substitution" in ISO/IEC 9899.

#define FragmentShaderFunc(useColorM, filter, address) \
  FragmentShaderFuncCp(useColorM, filter, address)

#define FragmentShaderFuncCp(useColorM, filter, address) \
  fragment float4 FragmentShader_##useColorM##_##filter##_##address( \
      VertexOut v [[stage_in]], \
      texture2d<float> texture [[texture(0)]], \
      constant float2& source_size [[buffer(2)]], \
      constant float4x4& color_matrix_body [[buffer(3)]], \
      constant float4& color_matrix_translation [[buffer(4)]], \
      constant float& scale [[buffer(5)]], \
      constant float4& source_region [[buffer(6)]]) { \
    return FragmentShaderImpl<useColorM, filter, address>().Do( \
        v, texture, source_size, color_matrix_body, color_matrix_translation, scale, source_region); \
  }

FragmentShaderFunc(0, FILTER_NEAREST, ADDRESS_CLAMP_TO_ZERO)
FragmentShaderFunc(0, FILTER_LINEAR, ADDRESS_CLAMP_TO_ZERO)
FragmentShaderFunc(0, FILTER_NEAREST, ADDRESS_REPEAT)
FragmentShaderFunc(0, FILTER_LINEAR, ADDRESS_REPEAT)
FragmentShaderFunc(0, FILTER_NEAREST, ADDRESS_UNSAFE)
FragmentShaderFunc(0, FILTER_LINEAR, ADDRESS_UNSAFE)
FragmentShaderFunc(1, FILTER_NEAREST, ADDRESS_CLAMP_TO_ZERO)
FragmentShaderFunc(1, FILTER_LINEAR, ADDRESS_CLAMP_TO_ZERO)
FragmentShaderFunc(1, FILTER_NEAREST, ADDRESS_REPEAT)
FragmentShaderFunc(1, FILTER_LINEAR, ADDRESS_REPEAT)
FragmentShaderFunc(1, FILTER_NEAREST, ADDRESS_UNSAFE)
FragmentShaderFunc(1, FILTER_LINEAR, ADDRESS_UNSAFE)

FragmentShaderFunc(0, FILTER_SCREEN, ADDRESS_UNSAFE)

#undef FragmentShaderFuncName
`

type rpsKey struct {
	useColorM     bool
	filter        driver.Filter
	address       driver.Address
	compositeMode driver.CompositeMode
	screen        bool
}

type Graphics struct {
	view view

	screenRPS mtl.RenderPipelineState
	rpss      map[rpsKey]mtl.RenderPipelineState
	cq        mtl.CommandQueue
	cb        mtl.CommandBuffer

	screenDrawable ca.MetalDrawable

	vb mtl.Buffer
	ib mtl.Buffer

	images      map[driver.ImageID]*Image
	nextImageID driver.ImageID

	shaders      map[driver.ShaderID]*Shader
	nextShaderID driver.ShaderID

	src *Image
	dst *Image

	transparent  bool
	maxImageSize int
	tmpTextures  []mtl.Texture

	pool unsafe.Pointer
}

var theGraphics Graphics

func Get() *Graphics {
	return &theGraphics
}

func (g *Graphics) Begin() {
	// NSAutoreleasePool is required to release drawable correctly (#847).
	// https://developer.apple.com/library/archive/documentation/3DDrawing/Conceptual/MTLBestPracticesGuide/Drawables.html
	g.pool = C.allocAutoreleasePool()
}

func (g *Graphics) End() {
	g.flushIfNeeded(true)
	g.screenDrawable = ca.MetalDrawable{}
	C.releaseAutoreleasePool(g.pool)
	g.pool = nil
}

func (g *Graphics) SetWindow(window uintptr) {
	// Note that [NSApp mainWindow] returns nil when the window is borderless.
	// Then the window is needed to be given explicitly.
	g.view.setWindow(window)
}

func (g *Graphics) SetUIView(uiview uintptr) {
	// TODO: Should this be called on the main thread?
	g.view.setUIView(uiview)
}

func (g *Graphics) SetVertices(vertices []float32, indices []uint16) {
	if g.vb != (mtl.Buffer{}) {
		g.vb.Release()
	}
	if g.ib != (mtl.Buffer{}) {
		g.ib.Release()
	}
	g.vb = g.view.getMTLDevice().MakeBufferWithBytes(unsafe.Pointer(&vertices[0]), unsafe.Sizeof(vertices[0])*uintptr(len(vertices)), resourceStorageMode)
	g.ib = g.view.getMTLDevice().MakeBufferWithBytes(unsafe.Pointer(&indices[0]), unsafe.Sizeof(indices[0])*uintptr(len(indices)), resourceStorageMode)
}

func (g *Graphics) flushIfNeeded(present bool) {
	if g.cb == (mtl.CommandBuffer{}) {
		return
	}

	if present && g.screenDrawable != (ca.MetalDrawable{}) {
		g.cb.PresentDrawable(g.screenDrawable)
	}
	g.cb.Commit()

	for _, t := range g.tmpTextures {
		t.Release()
	}
	g.tmpTextures = nil

	g.cb = mtl.CommandBuffer{}
}

func (g *Graphics) checkSize(width, height int) {
	if width < 1 {
		panic(fmt.Sprintf("metal: width (%d) must be equal or more than %d", width, 1))
	}
	if height < 1 {
		panic(fmt.Sprintf("metal: height (%d) must be equal or more than %d", height, 1))
	}
	m := g.MaxImageSize()
	if width > m {
		panic(fmt.Sprintf("metal: width (%d) must be less than or equal to %d", width, m))
	}
	if height > m {
		panic(fmt.Sprintf("metal: height (%d) must be less than or equal to %d", height, m))
	}
}

func (g *Graphics) genNextImageID() driver.ImageID {
	id := g.nextImageID
	g.nextImageID++
	return id
}

func (g *Graphics) InvalidImageID() driver.ImageID {
	return -1
}

func (g *Graphics) genNextShaderID() driver.ShaderID {
	id := g.nextShaderID
	g.nextShaderID++
	return id
}

func (g *Graphics) NewImage(width, height int) (driver.Image, error) {
	g.checkSize(width, height)
	td := mtl.TextureDescriptor{
		TextureType: mtl.TextureType2D,
		PixelFormat: mtl.PixelFormatRGBA8UNorm,
		Width:       graphics.InternalImageSize(width),
		Height:      graphics.InternalImageSize(height),
		StorageMode: storageMode,
		Usage:       mtl.TextureUsageShaderRead | mtl.TextureUsageRenderTarget,
	}
	t := g.view.getMTLDevice().MakeTexture(td)
	i := &Image{
		id:       g.genNextImageID(),
		graphics: g,
		width:    width,
		height:   height,
		texture:  t,
	}
	g.addImage(i)
	return i, nil
}

func (g *Graphics) NewScreenFramebufferImage(width, height int) (driver.Image, error) {
	g.view.setDrawableSize(width, height)
	i := &Image{
		id:       g.genNextImageID(),
		graphics: g,
		width:    width,
		height:   height,
		screen:   true,
	}
	g.addImage(i)
	return i, nil
}

func (g *Graphics) addImage(img *Image) {
	if g.images == nil {
		g.images = map[driver.ImageID]*Image{}
	}
	if _, ok := g.images[img.id]; ok {
		panic(fmt.Sprintf("opengl: image ID %d was already registered", img.id))
	}
	g.images[img.id] = img
}

func (g *Graphics) removeImage(img *Image) {
	delete(g.images, img.id)
}

func (g *Graphics) SetTransparent(transparent bool) {
	g.transparent = transparent
}

func operationToBlendFactor(c driver.Operation) mtl.BlendFactor {
	switch c {
	case driver.Zero:
		return mtl.BlendFactorZero
	case driver.One:
		return mtl.BlendFactorOne
	case driver.SrcAlpha:
		return mtl.BlendFactorSourceAlpha
	case driver.DstAlpha:
		return mtl.BlendFactorDestinationAlpha
	case driver.OneMinusSrcAlpha:
		return mtl.BlendFactorOneMinusSourceAlpha
	case driver.OneMinusDstAlpha:
		return mtl.BlendFactorOneMinusDestinationAlpha
	case driver.DstColor:
		return mtl.BlendFactorDestinationColor
	default:
		panic(fmt.Sprintf("metal: invalid operation: %d", c))
	}
}

func (g *Graphics) Reset() error {
	if g.cq != (mtl.CommandQueue{}) {
		g.cq.Release()
		g.cq = mtl.CommandQueue{}
	}

	// TODO: Release existing rpss
	if g.rpss == nil {
		g.rpss = map[rpsKey]mtl.RenderPipelineState{}
	}

	if err := g.view.reset(); err != nil {
		return err
	}
	if g.transparent {
		g.view.ml.SetOpaque(false)
	}

	replaces := map[string]string{
		"{{.FilterNearest}}":      fmt.Sprintf("%d", driver.FilterNearest),
		"{{.FilterLinear}}":       fmt.Sprintf("%d", driver.FilterLinear),
		"{{.FilterScreen}}":       fmt.Sprintf("%d", driver.FilterScreen),
		"{{.AddressClampToZero}}": fmt.Sprintf("%d", driver.AddressClampToZero),
		"{{.AddressRepeat}}":      fmt.Sprintf("%d", driver.AddressRepeat),
		"{{.AddressUnsafe}}":      fmt.Sprintf("%d", driver.AddressUnsafe),
	}
	src := source
	for k, v := range replaces {
		src = strings.Replace(src, k, v, -1)
	}

	lib, err := g.view.getMTLDevice().MakeLibrary(src, mtl.CompileOptions{})
	if err != nil {
		return err
	}
	vs, err := lib.MakeFunction("VertexShader")
	if err != nil {
		return err
	}
	fs, err := lib.MakeFunction(
		fmt.Sprintf("FragmentShader_%d_%d_%d", 0, driver.FilterScreen, driver.AddressUnsafe))
	if err != nil {
		return err
	}
	rpld := mtl.RenderPipelineDescriptor{
		VertexFunction:   vs,
		FragmentFunction: fs,
	}
	rpld.ColorAttachments[0].PixelFormat = g.view.colorPixelFormat()
	rpld.ColorAttachments[0].BlendingEnabled = true
	rpld.ColorAttachments[0].DestinationAlphaBlendFactor = mtl.BlendFactorZero
	rpld.ColorAttachments[0].DestinationRGBBlendFactor = mtl.BlendFactorZero
	rpld.ColorAttachments[0].SourceAlphaBlendFactor = mtl.BlendFactorOne
	rpld.ColorAttachments[0].SourceRGBBlendFactor = mtl.BlendFactorOne
	rps, err := g.view.getMTLDevice().MakeRenderPipelineState(rpld)
	if err != nil {
		return err
	}
	g.screenRPS = rps

	for _, screen := range []bool{false, true} {
		for _, cm := range []bool{false, true} {
			for _, a := range []driver.Address{
				driver.AddressClampToZero,
				driver.AddressRepeat,
				driver.AddressUnsafe,
			} {
				for _, f := range []driver.Filter{
					driver.FilterNearest,
					driver.FilterLinear,
				} {
					for c := driver.CompositeModeSourceOver; c <= driver.CompositeModeMax; c++ {
						cmi := 0
						if cm {
							cmi = 1
						}
						fs, err := lib.MakeFunction(fmt.Sprintf("FragmentShader_%d_%d_%d", cmi, f, a))
						if err != nil {
							return err
						}
						rpld := mtl.RenderPipelineDescriptor{
							VertexFunction:   vs,
							FragmentFunction: fs,
						}

						pix := mtl.PixelFormatRGBA8UNorm
						if screen {
							pix = g.view.colorPixelFormat()
						}
						rpld.ColorAttachments[0].PixelFormat = pix
						rpld.ColorAttachments[0].BlendingEnabled = true

						src, dst := c.Operations()
						rpld.ColorAttachments[0].DestinationAlphaBlendFactor = operationToBlendFactor(dst)
						rpld.ColorAttachments[0].DestinationRGBBlendFactor = operationToBlendFactor(dst)
						rpld.ColorAttachments[0].SourceAlphaBlendFactor = operationToBlendFactor(src)
						rpld.ColorAttachments[0].SourceRGBBlendFactor = operationToBlendFactor(src)
						rps, err := g.view.getMTLDevice().MakeRenderPipelineState(rpld)
						if err != nil {
							return err
						}
						g.rpss[rpsKey{
							screen:        screen,
							useColorM:     cm,
							filter:        f,
							address:       a,
							compositeMode: c,
						}] = rps
					}
				}
			}
		}
	}

	g.cq = g.view.getMTLDevice().MakeCommandQueue()
	return nil
}

func (g *Graphics) draw(rps mtl.RenderPipelineState, dst *Image, dstRegion driver.Region, srcs [graphics.ShaderImageNum]*Image, indexLen int, indexOffset int, uniforms []interface{}) error {
	g.view.update()

	rpd := mtl.RenderPassDescriptor{}
	// Even though the destination pixels are not used, mtl.LoadActionDontCare might cause glitches
	// (#1019). Always using mtl.LoadActionLoad is safe.
	rpd.ColorAttachments[0].LoadAction = mtl.LoadActionLoad
	rpd.ColorAttachments[0].StoreAction = mtl.StoreActionStore

	var t mtl.Texture
	if dst.screen {
		if g.screenDrawable == (ca.MetalDrawable{}) {
			drawable := g.view.drawable()
			if drawable == (ca.MetalDrawable{}) {
				return nil
			}
			g.screenDrawable = drawable
		}
		t = g.screenDrawable.Texture()
	} else {
		t = dst.texture
	}
	rpd.ColorAttachments[0].Texture = t
	rpd.ColorAttachments[0].ClearColor = mtl.ClearColor{}

	if g.cb == (mtl.CommandBuffer{}) {
		g.cb = g.cq.MakeCommandBuffer()
	}
	rce := g.cb.MakeRenderCommandEncoder(rpd)
	rce.SetRenderPipelineState(rps)

	// In Metal, the NDC's Y direction (upward) and the framebuffer's Y direction (downward) don't
	// match. Then, the Y direction must be inverted.
	w, h := dst.internalSize()
	rce.SetViewport(mtl.Viewport{
		OriginX: 0,
		OriginY: float64(h),
		Width:   float64(w),
		Height:  -float64(h),
		ZNear:   -1,
		ZFar:    1,
	})
	rce.SetScissorRect(mtl.ScissorRect{
		X:      int(dstRegion.X),
		Y:      int(dstRegion.Y),
		Width:  int(dstRegion.Width),
		Height: int(dstRegion.Height),
	})
	rce.SetVertexBuffer(g.vb, 0, 0)

	for i, u := range uniforms {
		switch u := u.(type) {
		case float32:
			rce.SetVertexBytes(unsafe.Pointer(&u), unsafe.Sizeof(u), i+1)
			rce.SetFragmentBytes(unsafe.Pointer(&u), unsafe.Sizeof(u), i+1)
		case []float32:
			rce.SetVertexBytes(unsafe.Pointer(&u[0]), unsafe.Sizeof(u[0])*uintptr(len(u)), i+1)
			rce.SetFragmentBytes(unsafe.Pointer(&u[0]), unsafe.Sizeof(u[0])*uintptr(len(u)), i+1)
		default:
			return fmt.Errorf("metal: unexpected uniform value: %[1]v (type: %[1]T)", u)
		}
	}

	for i, src := range srcs {
		if src != nil {
			rce.SetFragmentTexture(src.texture, i)
		} else {
			rce.SetFragmentTexture(mtl.Texture{}, i)
		}
	}
	rce.DrawIndexedPrimitives(mtl.PrimitiveTypeTriangle, indexLen, mtl.IndexTypeUInt16, g.ib, indexOffset*2)
	rce.EndEncoding()
	return nil
}

func (g *Graphics) Draw(dstID, srcID driver.ImageID, indexLen int, indexOffset int, mode driver.CompositeMode, colorM *affine.ColorM, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region) error {
	dst := g.images[dstID]
	dst.waitUntilSyncFinishes()

	srcs := [graphics.ShaderImageNum]*Image{g.images[srcID]}

	var rps mtl.RenderPipelineState
	if dst.screen && filter == driver.FilterScreen {
		rps = g.screenRPS
	} else {
		rps = g.rpss[rpsKey{
			screen:        dst.screen,
			useColorM:     colorM != nil,
			filter:        filter,
			address:       address,
			compositeMode: mode,
		}]
	}

	w, h := dst.internalSize()
	sourceSize := []float32{0, 0}
	if filter != driver.FilterNearest {
		w, h := srcs[0].internalSize()
		sourceSize[0] = float32(w)
		sourceSize[1] = float32(h)
	}
	esBody, esTranslate := colorM.UnsafeElements()
	scale := float32(0)
	if filter == driver.FilterScreen {
		scale = float32(dst.width) / float32(srcs[0].width)
	}
	uniforms := []interface{}{
		[]float32{float32(w), float32(h)},
		sourceSize,
		esBody,
		esTranslate,
		scale,
		[]float32{
			srcRegion.X,
			srcRegion.Y,
			srcRegion.X + srcRegion.Width,
			srcRegion.Y + srcRegion.Height,
		},
	}
	if err := g.draw(rps, dst, dstRegion, srcs, indexLen, indexOffset, uniforms); err != nil {
		return err
	}
	return nil
}

func (g *Graphics) SetVsyncEnabled(enabled bool) {
	g.view.setDisplaySyncEnabled(enabled)
}

func (g *Graphics) FramebufferYDirection() driver.YDirection {
	return driver.Downward
}

func (g *Graphics) NeedsRestoring() bool {
	return false
}

func (g *Graphics) IsGL() bool {
	return false
}

func (g *Graphics) HasHighPrecisionFloat() bool {
	return true
}

func (g *Graphics) MaxImageSize() int {
	if g.maxImageSize == 0 {
		g.maxImageSize = 4096
		// https://developer.apple.com/metal/Metal-Feature-Set-Tables.pdf
		switch {
		case g.view.getMTLDevice().SupportsFeatureSet(mtl.FeatureSet_iOS_GPUFamily5_v1):
			g.maxImageSize = 16384
		case g.view.getMTLDevice().SupportsFeatureSet(mtl.FeatureSet_iOS_GPUFamily4_v1):
			g.maxImageSize = 16384
		case g.view.getMTLDevice().SupportsFeatureSet(mtl.FeatureSet_iOS_GPUFamily3_v1):
			g.maxImageSize = 16384
		case g.view.getMTLDevice().SupportsFeatureSet(mtl.FeatureSet_iOS_GPUFamily2_v2):
			g.maxImageSize = 8192
		case g.view.getMTLDevice().SupportsFeatureSet(mtl.FeatureSet_iOS_GPUFamily2_v1):
			g.maxImageSize = 4096
		case g.view.getMTLDevice().SupportsFeatureSet(mtl.FeatureSet_iOS_GPUFamily1_v2):
			g.maxImageSize = 8192
		case g.view.getMTLDevice().SupportsFeatureSet(mtl.FeatureSet_iOS_GPUFamily1_v1):
			g.maxImageSize = 4096
		case g.view.getMTLDevice().SupportsFeatureSet(mtl.FeatureSet_tvOS_GPUFamily2_v1):
			g.maxImageSize = 16384
		case g.view.getMTLDevice().SupportsFeatureSet(mtl.FeatureSet_tvOS_GPUFamily1_v1):
			g.maxImageSize = 8192
		case g.view.getMTLDevice().SupportsFeatureSet(mtl.FeatureSet_macOS_GPUFamily1_v1):
			g.maxImageSize = 16384
		default:
			panic("metal: there is no supported feature set")
		}
	}
	return g.maxImageSize
}

func (g *Graphics) NewShader(program *shaderir.Program) (driver.Shader, error) {
	s, err := newShader(g.view.getMTLDevice(), g.genNextShaderID(), program)
	if err != nil {
		return nil, err
	}
	g.addShader(s)
	return s, nil
}

func (g *Graphics) addShader(shader *Shader) {
	if g.shaders == nil {
		g.shaders = map[driver.ShaderID]*Shader{}
	}
	if _, ok := g.shaders[shader.id]; ok {
		panic(fmt.Sprintf("metal: shader ID %d was already registered", shader.id))
	}
	g.shaders[shader.id] = shader
}

func (g *Graphics) removeShader(shader *Shader) {
	delete(g.shaders, shader.id)
}

type Image struct {
	id       driver.ImageID
	graphics *Graphics
	width    int
	height   int
	screen   bool
	texture  mtl.Texture
	sync     <-chan struct{}
}

func (i *Image) waitUntilSyncFinishes() {
	if i.sync == nil {
		return
	}
	<-i.sync
	i.sync = nil
}

func (i *Image) ID() driver.ImageID {
	return i.id
}

func (i *Image) internalSize() (int, int) {
	if i.screen {
		return i.width, i.height
	}
	return graphics.InternalImageSize(i.width), graphics.InternalImageSize(i.height)
}

func (i *Image) Dispose() {
	// TODO: Is it necessary to wait for syncing?
	i.waitUntilSyncFinishes()

	if i.texture != (mtl.Texture{}) {
		i.texture.Release()
		i.texture = mtl.Texture{}
	}
	i.graphics.removeImage(i)
}

func (i *Image) IsInvalidated() bool {
	// TODO: Does Metal cause context lost?
	// https://developer.apple.com/documentation/metal/mtlresource/1515898-setpurgeablestate
	// https://developer.apple.com/documentation/metal/mtldevicenotificationhandler
	return false
}

func (i *Image) Sync() <-chan struct{} {
	if i.sync != nil {
		return i.sync
	}

	i.graphics.flushIfNeeded(false)

	// Calling SynchronizeTexture is ignored on iOS (see mtl.m), but it looks like committing BlitCommandEncoder
	// is necessary (#1337).
	if i.graphics.cb != (mtl.CommandBuffer{}) {
		panic("metal: command buffer must be empty at syncTexture: flushIfNeeded is not called yet?")
	}

	cb := i.graphics.cq.MakeCommandBuffer()
	bce := cb.MakeBlitCommandEncoder()
	bce.SynchronizeTexture(i.texture, 0, 0)
	bce.EndEncoding()

	ch := make(chan struct{})
	cb.AddCompletedHandler(func() {
		close(ch)
	})
	cb.Commit()

	i.sync = ch
	return i.sync
}

func (i *Image) Pixels() ([]byte, error) {
	// Call Sync just in case when the user doesn't call Sync.
	// If the image is already synced, the channel should be closed immediately.
	<-i.Sync()
	i.sync = nil

	b := make([]byte, 4*i.width*i.height)
	i.texture.GetBytes(&b[0], uintptr(4*i.width), mtl.Region{
		Size: mtl.Size{Width: i.width, Height: i.height, Depth: 1},
	}, 0)
	return b, nil
}

func (i *Image) ReplacePixels(args []*driver.ReplacePixelsArgs) {
	i.waitUntilSyncFinishes()

	g := i.graphics

	// Use a temporary texture to send pixels asynchrounsly, whichever the memory is shared (e.g., iOS) or
	// managed (e.g., macOS). (#1418)
	w, h := i.texture.Width(), i.texture.Height()
	td := mtl.TextureDescriptor{
		TextureType: mtl.TextureType2D,
		PixelFormat: mtl.PixelFormatRGBA8UNorm,
		Width:       w,
		Height:      h,
		StorageMode: storageMode,
		Usage:       mtl.TextureUsageShaderRead | mtl.TextureUsageRenderTarget,
	}
	t := g.view.getMTLDevice().MakeTexture(td)
	g.tmpTextures = append(g.tmpTextures, t)

	for _, a := range args {
		t.ReplaceRegion(mtl.Region{
			Origin: mtl.Origin{X: a.X, Y: a.Y, Z: 0},
			Size:   mtl.Size{Width: a.Width, Height: a.Height, Depth: 1},
		}, 0, unsafe.Pointer(&a.Pixels[0]), 4*a.Width)
	}

	if g.cb == (mtl.CommandBuffer{}) {
		g.cb = i.graphics.cq.MakeCommandBuffer()
	}
	bce := g.cb.MakeBlitCommandEncoder()
	for _, a := range args {
		o := mtl.Origin{X: a.X, Y: a.Y, Z: 0}
		s := mtl.Size{Width: a.Width, Height: a.Height, Depth: 1}
		bce.CopyFromTexture(t, 0, 0, o, s, i.texture, 0, 0, o)
	}
	bce.EndEncoding()
}

func (g *Graphics) DrawShader(dstID driver.ImageID, srcIDs [graphics.ShaderImageNum]driver.ImageID, offsets [graphics.ShaderImageNum - 1][2]float32, shader driver.ShaderID, indexLen int, indexOffset int, dstRegion, srcRegion driver.Region, mode driver.CompositeMode, uniforms []interface{}) error {
	dst := g.images[dstID]
	dst.waitUntilSyncFinishes()

	var srcs [graphics.ShaderImageNum]*Image
	for i, srcID := range srcIDs {
		srcs[i] = g.images[srcID]
	}

	rps, err := g.shaders[shader].RenderPipelineState(g.view.getMTLDevice(), mode)
	if err != nil {
		return err
	}

	us := make([]interface{}, graphics.PreservedUniformVariablesNum+len(uniforms))

	// Set the destination texture size.
	dw, dh := dst.internalSize()
	us[graphics.DestinationTextureSizeUniformVariableIndex] = []float32{float32(dw), float32(dh)}

	// Set the source texture sizes.
	usizes := make([]float32, 2*len(srcs))
	for i, src := range srcs {
		if src != nil {
			w, h := src.internalSize()
			usizes[2*i] = float32(w)
			usizes[2*i+1] = float32(h)
		}
	}
	us[graphics.TextureSizesUniformVariableIndex] = usizes

	// Set the source offsets.
	uoffsets := make([]float32, 2*len(offsets))
	for i, offset := range offsets {
		uoffsets[2*i] = offset[0]
		uoffsets[2*i+1] = offset[1]
	}
	us[graphics.TextureSourceOffsetsUniformVariableIndex] = uoffsets

	// Set the source region's origin of texture0.
	uorigin := []float32{float32(srcRegion.X), float32(srcRegion.Y)}
	us[graphics.TextureSourceRegionOriginUniformVariableIndex] = uorigin

	// Set the source region's size of texture0.
	ussize := []float32{float32(srcRegion.Width), float32(srcRegion.Height)}
	us[graphics.TextureSourceRegionSizeUniformVariableIndex] = ussize

	// Set the additional uniform variables.
	for i, v := range uniforms {
		const offset = graphics.PreservedUniformVariablesNum
		us[offset+i] = v
	}

	if err := g.draw(rps, dst, dstRegion, srcs, indexLen, indexOffset, us); err != nil {
		return err
	}
	return nil
}