What differs between them

since 0.2.0 Backends

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Every other page in this showcase asks the device a capability question before it draws something that depends on the answer. This page is the list those questions come from, read live off whichever device is actually open.

Step 1: Ask every question #

GraphicsDevice has one getter per capability the engine ever needs to decide with: wireframe, cube textures, mip maps, rendering into a mip level, a stencil buffer, a blend constant and offscreen multisampling, plus three numbers rather than yes-or-no answers.

List<(String, String)> _rows(GraphicsDevice device) => <(String, String)>[
  ('wireframe', '${device.supportsWireframe}'),
  ('cube textures', '${device.supportsCubeTextures}'),
  ('mip maps', '${device.supportsMipmaps}'),
  ('render into a mip level', '${device.supportsRenderToMip}'),
  ('a stencil buffer', '${device.supportsStencil}'),
  ('a blend constant', '${device.supportsBlendColor}'),
  ('offscreen MSAA', '${device.supportsOffscreenMsaa}'),
  ('max anisotropy', '${device.maxAnisotropy}'),
  ('max colour attachments', '${device.maxColorAttachments}'),
  ('preferred sample count', '${device.preferredSampleCount}'),
];

Step 2: Where a number says more than yes or no #

Anisotropic filtering and multiple colour attachments are not yes-or-no questions. "Does it work" and "how much" are different questions, and a device that only answered the first would still leave a caller guessing how far to push it. maxAnisotropy and maxColorAttachments answer both at once, as does preferredSampleCount for multisampling.

List<(String, String)> _rows(GraphicsDevice device) => <(String, String)>[
  ('wireframe', '${device.supportsWireframe}'),
  ('cube textures', '${device.supportsCubeTextures}'),
  ('mip maps', '${device.supportsMipmaps}'),
  ('render into a mip level', '${device.supportsRenderToMip}'),
  ('a stencil buffer', '${device.supportsStencil}'),
  ('a blend constant', '${device.supportsBlendColor}'),
  ('offscreen MSAA', '${device.supportsOffscreenMsaa}'),
  ('max anisotropy', '${device.maxAnisotropy}'),
  ('max colour attachments', '${device.maxColorAttachments}'),
  ('preferred sample count', '${device.preferredSampleCount}'),
];

Note. Nothing on this page reads the device's name or its runtime type. Every line in the table above comes from asking a question the interface defines, which is the same rule every other page in this showcase follows.

Step 3: It should not drift mid-frame #

A capability is a property of the device, not of the frame that happened to run. Reading the same questions again after a frame has drawn has to give back the same answers this page started with.

// The capability report this page showed at build time has to still
// agree with a fresh reading of the same device after a frame has run.
// A backend's answers are a property of the device, not something a
// frame could have changed.
final CapabilityReport now = CapabilityReport.of(_device);
if (!now.met.containsAll(_atBuild.met) ||
    !_atBuild.met.containsAll(now.met)) {
  throw StateError(
    'the device answered a capability differently after a frame',
  );
}