WebGPU makes render targets/framebuffer objects easy. There is no need for an API to be built on top as a RenderPassEncoder is essentially a render target. Instead of rendering the surface frame, as we usually do, we can create an EmptyTexture of a specified size and use it as the output in a render pass.
EmptyTexture
Creates a new Texture of size 256, 256.
val preferredFormat = graphics.preferredFormat
val target = EmptyTexture(device, preferredFormat, 256, 256)
Rendering to a Texture
Render to a texture.
val commandEncoder = device.createCommandEncoder("command encoder")
val renderTargetRenderPass =
commandEncoder.beginRenderPass(
RenderPassDescriptor(
listOf(
RenderPassColorAttachmentDescriptor(
view = target.view, // our texture specified here!
loadOp = LoadOp.CLEAR,
storeOp = StoreOp.STORE,
clearColor =
if (preferredFormat.srgb) Color.YELLOW.toLinear()
else Color.YELLOW
)
),
label = "Surface render pass"
)
)
batch.begin()
batch.draw(mySprite, 0f, 0f) // we are drawing to the render target
batch.flush(renderTargetRenderPass)
renderTargetRenderPass.end()
val surfaceRenderPass =
commandEncoder.beginRenderPass(
RenderPassDescriptor(
listOf(
RenderPassColorAttachmentDescriptor(
view = frame,
loadOp = LoadOp.CLEAR,
storeOp = StoreOp.STORE,
clearColor =
if (preferredFormat.srgb) Color.DARK_GRAY.toLinear()
else Color.DARK_GRAY
)
),
label = "Surface render pass"
)
)
// now we draw the render target ouput to the surface frame
batch.draw(
target,
0f,
0f,
originX = target.width * 0.5f,
originY = target.height * 0.5f,
)
batch.flush(surfaceRenderPass)
batch.end()
surfaceRenderPass.end()