bazalt 0.8.0

Python library for rapid GPU shader prototyping using Vulkan

Bazalt

Bazalt is a modern Python library for rapid prototyping and building graphical applications using the Vulkan API. It provides a clean, intuitive interface over a high-performance C++ core, allowing developers to create rendering applications quickly without the typical boilerplate.

Installation

You can install bazalt easily via pip:

pip install bazalt

Prebuilt wheels are provided for Windows and Linux. Building from source requires a C++23 compiler — GCC 14+ or MSVC 19.36+ (Visual Studio 17.6) — and the Vulkan SDK.

Key Features

• Modern Graphics API: Built on top of Vulkan for optimal hardware utilization.
• Easy to Use Interface: Write clear and concise code with an intuitive API.
• Automatic Shader Compilation: Compile GLSL shaders (Vertex/Fragment/Compute) directly from your code.
• Compute Pipelines: ctx.compute_pipeline() + cmd.dispatch() — run GPU compute with results straight back into NumPy, no images required.
• Automatic Barriers: Hazards between resources (dispatch → dispatch, compute-written buffer → vertex fetch) get their barriers computed at record time. Context(auto_barriers=False) hands you full manual control via cmd.barrier().
• Pipeline & Buffer Management: Easy builder pattern for graphics pipelines and unified buffer creation.
• Command Buffers: Explicit, yet simple command recording — calls chain (cmd.bind_pipeline(p).draw(3)), and with cmd.rendering(target): closes the pass for you.
• Asynchronous Texture Streaming: ctx.load_image() returns immediately while the decode and GPU copy run in the background; anything that samples the image waits for it automatically. ctx.upload_progress gives you a loading bar for free.
• Hot Reload: Context(hot_reload=True) watches the shaders (and their #includes) and images you loaded and applies edits live — shaders recompile and rebuild their pipelines in place, images re-upload into the same handle. A typo or a bad file is logged and the last good version keeps rendering, so a mistake never takes the app down. See examples/12_hot_reload.
• Frame Timing & Debug Names: Context(gpu_timing=True) makes frame.gpu_time_ms report the GPU time of a recent frame (opt-in — off by default it costs nothing); name= / .name() label buffers, images and pipelines so validation messages name the culprit.
• Headless Rendering: Draw into an offscreen RenderTarget and read the pixels back as a NumPy array — no window, no display required.
• Render-to-Texture, MRT & Shadow Maps: Target attachments are ordinary Image objects in any supported Format — sample target.color[0] or a depth-only target's target.depth like any texture.
• Runs Widely: Vulkan 1.2 baseline with 1.3 used where available, so bazalt runs on older integrated GPUs too. Capabilities are requested by name, never by version or extension.
• Decoupled Architecture: Clean separation of concerns between Windowing (GLFW), Vulkan Context (GPU initialization), and render targets — a window is one target among others.

Quick Start: Rendering Without a Window

Everything below works with no display attached, which makes it usable from CI and tests:

import bazalt as bz

ctx = bz.Context()
target = bz.RenderTarget(ctx, 800, 600, depth=bz.Format.D32F)

pipeline = (ctx.graphics_pipeline()
    .vertex_shader(ctx.compile_shader("triangle.vert", bz.ShaderStage.VERTEX))
    .fragment_shader(ctx.compile_shader("triangle.frag", bz.ShaderStage.FRAGMENT))
    .vertex_format([bz.VertexFormat.FLOAT3, bz.VertexFormat.FLOAT3])
    .build(target))

# Interleaved position (x,y,z) and color (r,g,b)
vbuf = ctx.create_buffer([
     0.0, -0.5, 0.0,   1.0, 0.0, 0.0,
    -0.5,  0.5, 0.0,   0.0, 1.0, 0.0,
     0.5,  0.5, 0.0,   0.0, 0.0, 1.0,
], bz.BufferType.VERTEX, bz.MemoryUsage.STATIC, bz.DataType.FLOAT)

cmd = ctx.create_command_buffer()
cmd.begin()
with cmd.rendering(target, clear_color=[0.1, 0.2, 0.3, 1.0]) as c:
    c.bind_pipeline(pipeline).bind_vertex_buffer(vbuf).draw(3)

ctx.submit(cmd)

pixels = target.read_pixels()   # numpy (600, 800, 4) uint8

Quick Start: GPU Compute

Compute needs no window and no images — dispatch, then read the storage buffer back as a NumPy array:

import numpy as np
import bazalt as bz

ctx = bz.Context()

# double.comp: values[i] *= 2.0 over a std430 float array, local_size_x = 64
sim = (ctx.compute_pipeline()
    .shader(ctx.compile_shader("double.comp", bz.ShaderStage.COMPUTE))
    .storage_buffer(0)      # no stage argument — compute has exactly one stage
    .build())               # no target — compute has no attachments

data = np.arange(128, dtype=np.float32)
sbuf = ctx.create_buffer(data, bz.BufferType.STORAGE, bz.MemoryUsage.STATIC)

pool = ctx.create_descriptor_pool(max_sets=4, storage_buffers=4)
dset = pool.allocate_set(sim, set=0)
dset.set_buffer(0, sbuf)

cmd = ctx.create_command_buffer()
cmd.begin()
cmd.bind_pipeline(sim).bind_descriptor_set(dset, sim, set=0).dispatch(128 // 64)
ctx.submit(cmd)

assert np.allclose(sbuf.read(np.float32), data * 2)

Compute mixes freely with rendering in one command buffer — a dispatch that writes vertices and a draw that consumes them need no ceremony; the barrier between them is recorded automatically (see examples/11_particles).

Quick Start: Hot Reload

Add one keyword and bazalt watches the files it loaded — shaders (and their #includes) and images — recompiling and re-uploading on save:

ctx = bz.Context(logger, hot_reload=True)

vert = ctx.compile_shader("shader.vert", bz.ShaderStage.VERTEX)
frag = ctx.compile_shader("shader.frag", bz.ShaderStage.FRAGMENT)
tex  = ctx.load_image("wall.png")
pipeline = ctx.graphics_pipeline().vertex_shader(vert).fragment_shader(frag)...build(renderer)

while window.is_open():
    window.poll_events()
    if frame := renderer.begin_frame():   # edits are applied here (and at ctx.submit)
        frame.submit(cmd)                 # ...frame.gpu_time_ms (with gpu_timing=True) gives GPU frame timing

Editing shader.frag rebuilds the pipeline in place; re-saving wall.png (same size and format) re-uploads into the same handle, so descriptor sets need no rewrite. A shader typo logs a ShaderError and the last good pipeline keeps rendering — a mistake never crashes the app. Full demo: examples/12_hot_reload.

Quick Start: Drawing a Triangle

Here is a minimal example demonstrating how to initialize the window, Vulkan Context, and SwapchainRenderer, compile shaders, create a pipeline, and draw a colorful triangle.

import bazalt as bz

# 1. Initialize Logger and register a callback.
#    Each message carries its severity and source as data, so you can filter
#    without parsing strings. This is optional: a Context created without one
#    reports warnings on stderr by default.
logger = bz.Logger(min_severity=bz.Severity.WARNING)
@logger.on_message
def on_message(msg):
    print(f"[{msg.severity}] {msg.text}")

# 2. Create the window, Vulkan Context, and SwapchainRenderer
window = bz.Window(1024, 720, "Bazalt Demo - Triangle", logger=logger)
ctx = bz.Context(logger)
renderer = bz.SwapchainRenderer(window, ctx)

if __name__ == "__main__":
    # Load and compile shaders. The vertex shader processes our geometry,
    # and the fragment shader determines the final color of the pixels.
    # Shaders are compiled through the Context.
    vert_spv = ctx.compile_shader("triangle.vert", bz.ShaderStage.VERTEX)
    frag_spv = ctx.compile_shader("triangle.frag", bz.ShaderStage.FRAGMENT)

    # The pipeline is a baked state object that tells the GPU how to interpret our data.
    # It is built against a render target, which supplies the color/depth formats.
    # A SwapchainRenderer is one, so is an offscreen RenderTarget — same call.
    pipeline = (ctx.graphics_pipeline()
        .vertex_shader(vert_spv)
        .fragment_shader(frag_spv)
        .vertex_format([bz.VertexFormat.FLOAT3, bz.VertexFormat.FLOAT3]) # Position + Color
        .build(renderer))

    # We interleave Position (x,y,z) and Color (r,g,b) in a single flat array.
    # Vulkan's Normalized Device Coordinates (NDC) range from -1 to 1,
    # where Y points downwards and X points to the right.
    vertices = [
         0.0, -0.5, 0.0,   1.0, 0.0, 0.0, # Top / Red
        -0.5,  0.5, 0.0,   0.0, 1.0, 0.0, # Bottom-Left / Green
         0.5,  0.5, 0.0,   0.0, 0.0, 1.0, # Bottom-Right / Blue
    ]
    
    # Create Vertex Buffer through the Context
    vbuf = ctx.create_buffer(vertices, bz.BufferType.VERTEX, bz.MemoryUsage.STATIC, bz.DataType.FLOAT)
    
    # Create Index Buffer through the Context
    ibuf = ctx.create_buffer([0, 1, 2], bz.BufferType.INDEX, bz.MemoryUsage.STATIC, bz.DataType.UINT32)

    # Command buffers store a sequence of commands for the GPU.
    # For a static triangle, we can record this buffer once during initialization 
    # and submit the same pre-recorded buffer every frame to save CPU time.
    cmd = ctx.create_command_buffer()

    cmd.begin()

    # begin_rendering names the target you are drawing into, clears it, and sets
    # a viewport and scissor covering it. Naming the target is what lets the same
    # code render to a window or to an offscreen image.
    cmd.begin_rendering(renderer, clear_color=[0.1, 0.2, 0.3, 1.0])

    # Bind the baked pipeline and the geometry buffers
    cmd.bind_pipeline(pipeline)
    cmd.bind_vertex_buffer(vbuf)
    cmd.bind_index_buffer(ibuf)

    # Draw 3 indices (1 triangle)
    cmd.draw_indexed(3)
    cmd.end_rendering(renderer)

    # Main game/rendering loop
    while window.is_open():
        window.poll_events()
        
        # begin_frame returns a Frame, or None when this frame should be
        # skipped (window minimized, mid-resize)
        if frame := renderer.begin_frame():
            frame.submit(cmd)