Add experimental MLX backend and engine with imagegen support (#13648)

* WIP - MLX backend with gemma3

* MLX: add cmake and go tag build toggles

To build the new MLX backend code:
  cmake --preset MLX
  cmake --build --preset MLX --parallel
  cmake --install build --component MLX
  go build -tags mlx .

Note: the main.go entrypoint for the MLX engine will change in a follow up commit.

* add experimental image generation runtime

* add experimental image generation runtime

* MLX: wire up cuda build for linux

* MLX: get dependencies correct and dedup

This is still too large for a unified github artifact, but is now "correct" for the mlx_cuda_v13
directory.

* fix relative link bug in dedup

* Add darwin build and readme

* add go build tag for mlx dependent code and wire up build_darwin.sh

* lint cleanup

* macos: build mlx for x86

This will be CPU only.

* cuda build instructions and fix drift from mlx bump

* stale comment

* Delete agent helper doc

* Clean up readme.md

* Revise README for tokenizer clarity and details

Updated README to clarify tokenizer functionality and removed correctness section.

---------

Co-authored-by: jmorganca <jmorganca@gmail.com>

x/imagegen/models/zimage/text_encoder.go

@@ -0,0 +1,296 @@
+//go:build mlx
+
+package zimage
+
+import (
+	"encoding/json"
+	"fmt"
+	"math"
+	"os"
+	"path/filepath"
+
+	"github.com/ollama/ollama/x/imagegen/mlx"
+	"github.com/ollama/ollama/x/imagegen/nn"
+	"github.com/ollama/ollama/x/imagegen/safetensors"
+	"github.com/ollama/ollama/x/imagegen/tokenizer"
+)
+
+// Qwen3Config holds Qwen3 text encoder configuration
+type Qwen3Config struct {
+	HiddenSize        int32   `json:"hidden_size"`
+	NumHiddenLayers   int32   `json:"num_hidden_layers"`
+	IntermediateSize  int32   `json:"intermediate_size"`
+	NumAttentionHeads int32   `json:"num_attention_heads"`
+	NumKeyValueHeads  int32   `json:"num_key_value_heads"`
+	VocabSize         int32   `json:"vocab_size"`
+	RMSNormEps        float32 `json:"rms_norm_eps"`
+	RopeTheta         float32 `json:"rope_theta"`
+	HeadDim           int32   `json:"head_dim"`
+}
+
+// loadQwen3Config loads text encoder config from a JSON file
+func loadQwen3Config(path string) (*Qwen3Config, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return nil, fmt.Errorf("read config: %w", err)
+	}
+	var cfg Qwen3Config
+	if err := json.Unmarshal(data, &cfg); err != nil {
+		return nil, fmt.Errorf("parse config: %w", err)
+	}
+	return &cfg, nil
+}
+
+// Qwen3Attention implements Qwen3 attention with QK norms
+type Qwen3Attention struct {
+	QProj *nn.Linear  `weight:"q_proj"`
+	KProj *nn.Linear  `weight:"k_proj"`
+	VProj *nn.Linear  `weight:"v_proj"`
+	OProj *nn.Linear  `weight:"o_proj"`
+	QNorm *nn.RMSNorm `weight:"q_norm"`
+	KNorm *nn.RMSNorm `weight:"k_norm"`
+	// Computed fields
+	NHeads    int32
+	NKVHeads  int32
+	HeadDim   int32
+	Scale     float32
+	RopeTheta float32
+}
+
+// applyRoPEQwen3 applies the custom RoPE for Qwen3 text encoder
+func applyRoPEQwen3(x *mlx.Array, seqLen int32, theta float32) *mlx.Array {
+	shape := x.Shape()
+	B := shape[0]
+	L := shape[1]
+	H := shape[2]
+	D := shape[3]
+	half := D / 2
+
+	freqsArr := make([]float32, half)
+	logTheta := float32(math.Log(float64(theta)))
+	for i := int32(0); i < half; i++ {
+		freqsArr[i] = float32(math.Exp(float64(-logTheta * float32(i) / float32(half))))
+	}
+	freqs := mlx.NewArray(freqsArr, []int32{half})
+
+	posArr := make([]float32, seqLen)
+	for i := int32(0); i < seqLen; i++ {
+		posArr[i] = float32(i)
+	}
+	pos := mlx.NewArray(posArr, []int32{seqLen})
+
+	posExpanded := mlx.Reshape(pos, seqLen, 1)
+	freqsExpanded := mlx.Reshape(freqs, 1, half)
+	args := mlx.Mul(posExpanded, freqsExpanded)
+
+	cosVals := mlx.Cos(args)
+	sinVals := mlx.Sin(args)
+	cosVals = mlx.Reshape(cosVals, seqLen, 1, half)
+	sinVals = mlx.Reshape(sinVals, seqLen, 1, half)
+
+	x1 := mlx.Slice(x, []int32{0, 0, 0, 0}, []int32{B, L, H, half})
+	x2 := mlx.Slice(x, []int32{0, 0, 0, half}, []int32{B, L, H, D})
+
+	part1 := mlx.Sub(mlx.Mul(x1, cosVals), mlx.Mul(x2, sinVals))
+	part2 := mlx.Add(mlx.Mul(x1, sinVals), mlx.Mul(x2, cosVals))
+
+	return mlx.Concatenate([]*mlx.Array{part1, part2}, 3)
+}
+
+// Forward computes attention with causal masking
+func (attn *Qwen3Attention) Forward(x *mlx.Array) *mlx.Array {
+	shape := x.Shape()
+	B := shape[0]
+	L := shape[1]
+
+	q := attn.QProj.Forward(x)
+	k := attn.KProj.Forward(x)
+	v := attn.VProj.Forward(x)
+
+	q = mlx.Reshape(q, B, L, attn.NHeads, attn.HeadDim)
+	k = mlx.Reshape(k, B, L, attn.NKVHeads, attn.HeadDim)
+	v = mlx.Reshape(v, B, L, attn.NKVHeads, attn.HeadDim)
+
+	// QK norm uses 1e-6 hardcoded (Qwen3 specific)
+	q = attn.QNorm.Forward(q, 1e-6)
+	k = attn.KNorm.Forward(k, 1e-6)
+
+	q = applyRoPEQwen3(q, L, attn.RopeTheta)
+	k = applyRoPEQwen3(k, L, attn.RopeTheta)
+
+	q = mlx.Transpose(q, 0, 2, 1, 3)
+	k = mlx.Transpose(k, 0, 2, 1, 3)
+	v = mlx.Transpose(v, 0, 2, 1, 3)
+
+	if attn.NKVHeads < attn.NHeads {
+		repeats := attn.NHeads / attn.NKVHeads
+		k = repeatKV(k, repeats)
+		v = repeatKV(v, repeats)
+	}
+
+	out := mlx.ScaledDotProductAttention(q, k, v, attn.Scale, true)
+
+	out = mlx.Transpose(out, 0, 2, 1, 3)
+	out = mlx.Reshape(out, B, L, attn.NHeads*attn.HeadDim)
+
+	out = attn.OProj.Forward(out)
+
+	return out
+}
+
+// repeatKV repeats key/value heads for GQA
+func repeatKV(x *mlx.Array, repeats int32) *mlx.Array {
+	if repeats == 1 {
+		return x
+	}
+	shape := x.Shape()
+	x = mlx.ExpandDims(x, 2)
+	x = mlx.Tile(x, []int32{1, 1, repeats, 1, 1})
+	return mlx.Reshape(x, shape[0], shape[1]*repeats, shape[2], shape[3])
+}
+
+// Qwen3MLP implements Qwen3 SwiGLU MLP
+type Qwen3MLP struct {
+	GateProj *nn.Linear `weight:"gate_proj"`
+	UpProj   *nn.Linear `weight:"up_proj"`
+	DownProj *nn.Linear `weight:"down_proj"`
+}
+
+// Forward applies the MLP
+func (m *Qwen3MLP) Forward(x *mlx.Array) *mlx.Array {
+	gate := m.GateProj.Forward(x)
+	gate = mlx.SiLU(gate)
+	up := m.UpProj.Forward(x)
+	h := mlx.Mul(gate, up)
+	return m.DownProj.Forward(h)
+}
+
+// Qwen3Block represents a single Qwen3 transformer block
+type Qwen3Block struct {
+	Attention         *Qwen3Attention `weight:"self_attn"`
+	MLP               *Qwen3MLP       `weight:"mlp"`
+	InputLayerNorm    *nn.RMSNorm     `weight:"input_layernorm"`
+	PostAttnLayerNorm *nn.RMSNorm     `weight:"post_attention_layernorm"`
+}
+
+// Forward applies the Qwen3 block
+func (qb *Qwen3Block) Forward(x *mlx.Array, eps float32) *mlx.Array {
+	h := qb.InputLayerNorm.Forward(x, eps)
+	attnOut := qb.Attention.Forward(h)
+	x = mlx.Add(x, attnOut)
+
+	h = qb.PostAttnLayerNorm.Forward(x, eps)
+	mlpOut := qb.MLP.Forward(h)
+	x = mlx.Add(x, mlpOut)
+
+	return x
+}
+
+// Qwen3TextEncoder is the full Qwen3 encoder for Z-Image
+type Qwen3TextEncoder struct {
+	EmbedTokens *nn.Embedding   `weight:"model.embed_tokens"`
+	Layers      []*Qwen3Block   `weight:"model.layers"`
+	FinalNorm   *nn.RMSNorm     `weight:"model.norm"`
+	*Qwen3Config
+}
+
+// Load loads the Qwen3 text encoder from a directory
+func (m *Qwen3TextEncoder) Load(path string) error {
+	fmt.Println("Loading Qwen3 text encoder...")
+
+	// Load config
+	cfg, err := loadQwen3Config(filepath.Join(path, "config.json"))
+	if err != nil {
+		return fmt.Errorf("config: %w", err)
+	}
+	m.Qwen3Config = cfg
+
+	// Pre-allocate layers slice
+	m.Layers = make([]*Qwen3Block, cfg.NumHiddenLayers)
+
+	// Load weights
+	weights, err := safetensors.LoadModelWeights(path)
+	if err != nil {
+		return fmt.Errorf("weights: %w", err)
+	}
+
+	fmt.Print("  Loading weights via struct tags... ")
+	if err := safetensors.LoadModule(m, weights, ""); err != nil {
+		return fmt.Errorf("load module: %w", err)
+	}
+	fmt.Println("✓")
+
+	// Initialize computed fields
+	m.FinalNorm.Eps = cfg.RMSNormEps
+	for _, block := range m.Layers {
+		// Attention
+		block.Attention.NHeads = cfg.NumAttentionHeads
+		block.Attention.NKVHeads = cfg.NumKeyValueHeads
+		block.Attention.HeadDim = cfg.HeadDim
+		block.Attention.Scale = float32(1.0 / math.Sqrt(float64(cfg.HeadDim)))
+		block.Attention.RopeTheta = cfg.RopeTheta
+		block.Attention.QNorm.Eps = cfg.RMSNormEps
+		block.Attention.KNorm.Eps = cfg.RMSNormEps
+		// Block norms
+		block.InputLayerNorm.Eps = cfg.RMSNormEps
+		block.PostAttnLayerNorm.Eps = cfg.RMSNormEps
+	}
+
+	weights.ReleaseAll()
+	return nil
+}
+
+// Forward encodes text tokens
+func (te *Qwen3TextEncoder) Forward(tokens *mlx.Array) *mlx.Array {
+	h := te.EmbedTokens.Forward(tokens)
+	eps := te.RMSNormEps
+
+	for _, layer := range te.Layers {
+		h = layer.Forward(h, eps)
+	}
+
+	// Apply final RMS norm
+	h = te.FinalNorm.Forward(h, eps)
+
+	return h
+}
+
+// ApplyChatTemplate wraps prompt in Qwen3 chat format
+func ApplyChatTemplate(prompt string) string {
+	return "<|im_start|>user\n" + prompt + "<|im_end|>\n<|im_start|>assistant\n"
+}
+
+// EncodePrompt encodes a text prompt using the tokenizer and encoder
+func (te *Qwen3TextEncoder) EncodePrompt(tok *tokenizer.Tokenizer, prompt string, maxLen int) (*mlx.Array, *mlx.Array) {
+	formattedPrompt := ApplyChatTemplate(prompt)
+
+	tokens := tok.Encode(formattedPrompt, false)
+
+	if len(tokens) > maxLen {
+		tokens = tokens[:maxLen]
+	}
+
+	maskData := make([]float32, maxLen)
+	for i := 0; i < len(tokens); i++ {
+		maskData[i] = 1.0
+	}
+
+	// Get PAD token (different from EOS for Qwen3)
+	padToken := tok.PAD()
+	if padToken < 0 {
+		padToken = tok.EOS() // fallback
+	}
+
+	paddedTokens := make([]int32, maxLen)
+	copy(paddedTokens, tokens)
+	for i := len(tokens); i < maxLen; i++ {
+		paddedTokens[i] = padToken
+	}
+
+	tokensArr := mlx.NewArrayInt32(paddedTokens, []int32{1, int32(maxLen)})
+	maskArr := mlx.NewArray(maskData, []int32{1, int32(maxLen)})
+
+	embeddings := te.Forward(tokensArr)
+
+	return embeddings, maskArr
+}