util/gpu/demo-metal.mm

/*
 * Copyright 2026 Behdad Esfahbod. All Rights Reserved.
 */

#ifdef __APPLE__

#include "demo-renderer.h"
#include "demo-atlas.h"
#include <hb-gpu.h>

#import <Metal/Metal.h>
#import <QuartzCore/CAMetalLayer.h>

#define GLFW_EXPOSE_NATIVE_COCOA
#include <GLFW/glfw3native.h>

#define TEXEL_SIZE 8  /* sizeof short4 texel */

#include "demo-shader-msl.hh"


struct demo_renderer_metal_t : demo_renderer_t
{
  GLFWwindow *window;
  bool draw_only;

  /* Metal objects */
  id<MTLDevice> device;
  id<MTLCommandQueue> commandQueue;
  id<MTLRenderPipelineState> pipelineState;
  id<MTLRenderPipelineState> blitPipelineState;
  CAMetalLayer *metalLayer;

  /* Offscreen render target for vsync-off mode */
  id<MTLTexture> offscreenTexture;
  int offscreen_w, offscreen_h;
  bool vsync_on;
  double last_present_time;

  /* Atlas (CPU shadow + GPU buffer) */
  demo_atlas_t *atlas;
  char *atlas_data;
  unsigned int atlas_capacity;  /* in texels */
  unsigned int atlas_cursor;    /* in texels */
  id<MTLBuffer> atlasBuffer;
  bool atlas_dirty;

  /* Cached vertex buffer */
  id<MTLBuffer> vertexBuffer;
  glyph_vertex_t *uploaded_ptr;
  unsigned int uploaded_count;

  /* Clear color */
  float bg[4];

  /* Uniforms — must match MSL Uniforms struct layout */
  struct {
    float matViewProjection[16];
    float viewport[2];
    float gamma;
    float stem_darkening;
    float foreground[4];
    float debug;
    float _pad[3];
  } uniforms;


  demo_renderer_metal_t (GLFWwindow *window_, bool draw_only_)
    : window (window_), draw_only (draw_only_)
  {
    uploaded_ptr = nullptr;
    uploaded_count = 0;
    offscreen_w = offscreen_h = 0;
    vsync_on = true;
    last_present_time = 0;
    bg[0] = bg[1] = bg[2] = bg[3] = 1.0f;
    memset (&uniforms, 0, sizeof (uniforms));
    uniforms.gamma = 1.0f;
    uniforms.foreground[3] = 1.0f;
    uniforms.stem_darkening = 1.0f;
  }

  ~demo_renderer_metal_t () override
  {
    demo_atlas_destroy (atlas);
    free (atlas_data);
  }


  /* -- Atlas -- */

  static unsigned int
  atlas_alloc_cb (void *ctx, const char *data, unsigned int len_bytes)
  {
    auto *self = (demo_renderer_metal_t *) ctx;
    unsigned int len_texels = len_bytes / TEXEL_SIZE;
    if (self->atlas_cursor + len_texels > self->atlas_capacity)
      die ("Ran out of atlas memory");
    unsigned int offset = self->atlas_cursor;
    self->atlas_cursor += len_texels;
    memcpy (self->atlas_data + offset * TEXEL_SIZE, data, len_bytes);
    self->atlas_dirty = true;
    return offset;
  }

  static unsigned int
  atlas_get_used_cb (void *ctx)
  {
    return ((demo_renderer_metal_t *) ctx)->atlas_cursor;
  }

  static void
  atlas_clear_cb (void *ctx)
  {
    auto *self = (demo_renderer_metal_t *) ctx;
    self->atlas_cursor = 0;
    self->atlas_dirty = true;
  }

  demo_atlas_t *get_atlas () override
  {
    return atlas;
  }

  /* -- State -- */

  void setup () override {}

  void set_gamma (float gamma) override
  {
    uniforms.gamma = gamma;
  }

  void set_foreground (float r, float g, float b, float a) override
  {
    uniforms.foreground[0] = r;
    uniforms.foreground[1] = g;
    uniforms.foreground[2] = b;
    uniforms.foreground[3] = a;
  }

  void set_background (float r, float g, float b, float a) override
  {
    bg[0] = r; bg[1] = g; bg[2] = b; bg[3] = a;
  }

  void set_debug (bool enabled) override
  {
    uniforms.debug = enabled ? 1.f : 0.f;
  }

  void set_stem_darkening (bool enabled) override
  {
    uniforms.stem_darkening = enabled ? 1.f : 0.f;
  }

  void toggle_vsync (bool &vsync) override
  {
    vsync = !vsync;
    vsync_on = vsync;
    metalLayer.displaySyncEnabled = vsync;
  }

  void ensure_offscreen (int width, int height)
  {
    if (offscreenTexture && offscreen_w == width && offscreen_h == height)
      return;
    MTLTextureDescriptor *desc =
      [MTLTextureDescriptor texture2DDescriptorWithPixelFormat:MTLPixelFormatBGRA8Unorm
							width:width
						       height:height
						    mipmapped:NO];
    desc.usage = MTLTextureUsageRenderTarget | MTLTextureUsageShaderRead;
    desc.storageMode = MTLStorageModePrivate;
    offscreenTexture = [device newTextureWithDescriptor:desc];
    offscreen_w = width;
    offscreen_h = height;
  }


  /* -- Frame -- */

  void display (glyph_vertex_t *vertices, unsigned int count,
		unsigned generation,
		int width, int height, float mat[16]) override
  {
    @autoreleasepool {

    /* Update layer size */
    CGSize size = { (CGFloat) width, (CGFloat) height };
    metalLayer.drawableSize = size;

    /* Update uniforms */
    memcpy (uniforms.matViewProjection, mat, 16 * sizeof (float));
    uniforms.viewport[0] = (float) width;
    uniforms.viewport[1] = (float) height;

    /* Sync atlas if dirty */
    if (atlas_dirty)
    {
      memcpy (atlasBuffer.contents, atlas_data,
	      atlas_cursor * TEXEL_SIZE);
      atlas_dirty = false;
    }

    /* Only re-upload vertices if data changed. */
    if (count > 0 && (vertices != uploaded_ptr || count != uploaded_count))
    {
      vertexBuffer = [device newBufferWithBytes:vertices
					length:count * sizeof (glyph_vertex_t)
				       options:MTLResourceStorageModeShared];
      uploaded_ptr = vertices;
      uploaded_count = count;
    }

    /*
     * When vsync is off, render to an offscreen texture (no blocking)
     * and blit to a drawable only when one is immediately available.
     * This decouples the render loop from the display refresh rate.
     */
    if (!vsync_on)
    {
      ensure_offscreen (width, height);

      /* Render to offscreen */
      MTLRenderPassDescriptor *passDesc = [MTLRenderPassDescriptor renderPassDescriptor];
      passDesc.colorAttachments[0].texture = offscreenTexture;
      passDesc.colorAttachments[0].loadAction = MTLLoadActionClear;
      passDesc.colorAttachments[0].storeAction = MTLStoreActionStore;
      passDesc.colorAttachments[0].clearColor = MTLClearColorMake ((double) bg[0], (double) bg[1], (double) bg[2], (double) bg[3]);

      id<MTLCommandBuffer> commandBuffer = [commandQueue commandBuffer];
      id<MTLRenderCommandEncoder> encoder =
	[commandBuffer renderCommandEncoderWithDescriptor:passDesc];

      [encoder setViewport:(MTLViewport){0, 0, (double) width, (double) height, 0, 1}];
      [encoder setRenderPipelineState:pipelineState];

      if (count > 0)
      {
	[encoder setVertexBuffer:vertexBuffer offset:0 atIndex:0];
	[encoder setVertexBytes:&uniforms length:sizeof (uniforms) atIndex:1];
	[encoder setFragmentBuffer:atlasBuffer offset:0 atIndex:0];
	[encoder setFragmentBytes:&uniforms length:sizeof (uniforms) atIndex:1];

	[encoder drawPrimitives:MTLPrimitiveTypeTriangle
		    vertexStart:0
		    vertexCount:count];
      }

      [encoder endEncoding];

      /* Present at most ~120 times/sec so the display stays live. */
      double now = glfwGetTime ();
      if (now - last_present_time > 1.0 / 120.0)
      {
	id<CAMetalDrawable> drawable = [metalLayer nextDrawable];
	if (drawable)
	{
	  id<MTLBlitCommandEncoder> blit = [commandBuffer blitCommandEncoder];
	  [blit copyFromTexture:offscreenTexture toTexture:drawable.texture];
	  [blit endEncoding];
	  [commandBuffer presentDrawable:drawable];
	  last_present_time = now;
	}
      }

      [commandBuffer commit];
    }
    else
    {
      /* Vsync on: render directly to drawable. */
      id<CAMetalDrawable> drawable = [metalLayer nextDrawable];
      if (!drawable)
	return;

      MTLRenderPassDescriptor *passDesc = [MTLRenderPassDescriptor renderPassDescriptor];
      passDesc.colorAttachments[0].texture = drawable.texture;
      passDesc.colorAttachments[0].loadAction = MTLLoadActionClear;
      passDesc.colorAttachments[0].storeAction = MTLStoreActionStore;
      passDesc.colorAttachments[0].clearColor = MTLClearColorMake ((double) bg[0], (double) bg[1], (double) bg[2], (double) bg[3]);

      id<MTLCommandBuffer> commandBuffer = [commandQueue commandBuffer];
      id<MTLRenderCommandEncoder> encoder =
	[commandBuffer renderCommandEncoderWithDescriptor:passDesc];

      [encoder setViewport:(MTLViewport){0, 0, (double) width, (double) height, 0, 1}];
      [encoder setRenderPipelineState:pipelineState];

      if (count > 0)
      {
	[encoder setVertexBuffer:vertexBuffer offset:0 atIndex:0];
	[encoder setVertexBytes:&uniforms length:sizeof (uniforms) atIndex:1];
	[encoder setFragmentBuffer:atlasBuffer offset:0 atIndex:0];
	[encoder setFragmentBytes:&uniforms length:sizeof (uniforms) atIndex:1];

	[encoder drawPrimitives:MTLPrimitiveTypeTriangle
		    vertexStart:0
		    vertexCount:count];
      }

      [encoder endEncoding];
      [commandBuffer presentDrawable:drawable];
      [commandBuffer commit];
    }

    } /* @autoreleasepool */
  }
};


demo_renderer_t *
demo_renderer_create_metal (GLFWwindow *window, bool draw_only)
{
  @autoreleasepool {

  auto *r = new demo_renderer_metal_t (window, draw_only);

  /* Get Metal device */
  r->device = MTLCreateSystemDefaultDevice ();
  if (!r->device)
  {
    delete r;
    return nullptr;
  }

  r->commandQueue = [r->device newCommandQueue];

  /* Set up CAMetalLayer on the GLFW window */
  NSWindow *nswindow = glfwGetCocoaWindow (window);
  r->metalLayer = [CAMetalLayer layer];
  r->metalLayer.device = r->device;
  r->metalLayer.pixelFormat = MTLPixelFormatBGRA8Unorm;
  nswindow.contentView.layer = r->metalLayer;
  nswindow.contentView.wantsLayer = YES;

  /* Compile shaders */
  const char *vert_common = hb_gpu_shader_source       (HB_GPU_SHADER_STAGE_VERTEX, HB_GPU_SHADER_LANG_MSL);
  const char *vert_src    = hb_gpu_draw_shader_source  (HB_GPU_SHADER_STAGE_VERTEX, HB_GPU_SHADER_LANG_MSL);
  const char *frag_common = hb_gpu_shader_source       (HB_GPU_SHADER_STAGE_FRAGMENT, HB_GPU_SHADER_LANG_MSL);
  const char *frag_mode   = draw_only
    ? hb_gpu_draw_shader_source  (HB_GPU_SHADER_STAGE_FRAGMENT, HB_GPU_SHADER_LANG_MSL)
    : hb_gpu_paint_shader_source (HB_GPU_SHADER_STAGE_FRAGMENT, HB_GPU_SHADER_LANG_MSL);

  NSString *preamble = draw_only
    ? @"#include <metal_stdlib>\nusing namespace metal;\n#define HB_GPU_DEMO_DRAW\n"
    : @"#include <metal_stdlib>\nusing namespace metal;\n";
  NSString *source = [NSString stringWithFormat:@"%@%s%s%s%s%s",
		      preamble, vert_common, vert_src,
		      frag_common, frag_mode,
		      demo_shader_msl];

  NSError *error = nil;
  id<MTLLibrary> library = [r->device newLibraryWithSource:source
						   options:nil
						     error:&error];
  if (!library)
  {
    fprintf (stderr, "Metal shader compilation failed: %s\n",
	     [[error localizedDescription] UTF8String]);
    delete r;
    return nullptr;
  }

  id<MTLFunction> vertexFunc = [library newFunctionWithName:@"vertex_main"];
  id<MTLFunction> fragmentFunc = [library newFunctionWithName:@"fragment_main"];

  /* Create vertex descriptor matching glyph_vertex_t layout */
  MTLVertexDescriptor *vertexDesc = [MTLVertexDescriptor vertexDescriptor];
  vertexDesc.attributes[0].format = MTLVertexFormatFloat2;
  vertexDesc.attributes[0].offset = 0;
  vertexDesc.attributes[0].bufferIndex = 0;
  vertexDesc.attributes[1].format = MTLVertexFormatFloat2;
  vertexDesc.attributes[1].offset = 8;
  vertexDesc.attributes[1].bufferIndex = 0;
  vertexDesc.attributes[2].format = MTLVertexFormatFloat2;
  vertexDesc.attributes[2].offset = 16;
  vertexDesc.attributes[2].bufferIndex = 0;
  vertexDesc.attributes[3].format = MTLVertexFormatFloat;
  vertexDesc.attributes[3].offset = 24;
  vertexDesc.attributes[3].bufferIndex = 0;
  vertexDesc.attributes[4].format = MTLVertexFormatUInt;
  vertexDesc.attributes[4].offset = 28;
  vertexDesc.attributes[4].bufferIndex = 0;
  vertexDesc.layouts[0].stride = 32;

  /* Create pipeline */
  MTLRenderPipelineDescriptor *pipelineDesc = [[MTLRenderPipelineDescriptor alloc] init];
  pipelineDesc.vertexFunction = vertexFunc;
  pipelineDesc.fragmentFunction = fragmentFunc;
  pipelineDesc.vertexDescriptor = vertexDesc;
  pipelineDesc.colorAttachments[0].pixelFormat = MTLPixelFormatBGRA8Unorm;
  pipelineDesc.colorAttachments[0].blendingEnabled = YES;
  pipelineDesc.colorAttachments[0].sourceRGBBlendFactor = MTLBlendFactorSourceAlpha;
  pipelineDesc.colorAttachments[0].destinationRGBBlendFactor = MTLBlendFactorOneMinusSourceAlpha;
  pipelineDesc.colorAttachments[0].sourceAlphaBlendFactor = MTLBlendFactorSourceAlpha;
  pipelineDesc.colorAttachments[0].destinationAlphaBlendFactor = MTLBlendFactorOneMinusSourceAlpha;

  error = nil;
  r->pipelineState = [r->device newRenderPipelineStateWithDescriptor:pipelineDesc
							       error:&error];
  if (!r->pipelineState)
  {
    fprintf (stderr, "Metal pipeline creation failed: %s\n",
	     [[error localizedDescription] UTF8String]);
    delete r;
    return nullptr;
  }

  /* Atlas */
  unsigned int atlas_capacity = 1024 * 1024;
  r->atlas_capacity = atlas_capacity;
  r->atlas_cursor = 0;
  r->atlas_data = (char *) calloc (atlas_capacity, TEXEL_SIZE);
  r->atlasBuffer = [r->device newBufferWithLength:atlas_capacity * TEXEL_SIZE
					  options:MTLResourceStorageModeShared];
  r->atlas_dirty = false;

  /* Create atlas wrapper for demo_font_t */
  demo_atlas_backend_t backend = {
    r,
    demo_renderer_metal_t::atlas_alloc_cb,
    demo_renderer_metal_t::atlas_get_used_cb,
    demo_renderer_metal_t::atlas_clear_cb,
  };
  r->atlas = demo_atlas_create_external (&backend);

  return r;

  } /* @autoreleasepool */
}

#endif /* __APPLE__ */