maszyna/docs/opengl46-renderer.md

OpenGL 4.6 renderer

The default renderer (gfxrenderer default, the modern backend, rendering/opengl46/) runs on an OpenGL 4.6 core profile context. There is no fallback to an older version, and the OpenGL 2.1 (legacy) renderer and the OpenGL ES / ANGLE path no longer exist.

For how the lights are handled, see clustered-lighting.md.

Requirements

• A graphics card and driver that provide OpenGL 4.6 (core profile). What the driver offers is written to the log at start: Renderer:, Vendor: and GL version:.
• A CPU with AVX2, as before.
• Windows and Linux. macOS provides OpenGL only up to 4.1, so the renderer does not run there.
• The experimental Better Renderer (gfxrenderer experimental) is a separate renderer and is not affected.

On Linux, glxinfo -B should report an OpenGL core profile version string of 4.6 or newer.

If the simulator does not start

When the context cannot be created, the log (log.txt) contains a line like

Bad init: failed to create OpenGL 4.6 core profile context (<GLFW error>); the graphics card/driver provides: OpenGL X.Y ..., <renderer> (<vendor>)

On Windows the same text is shown in a message box. Updating the graphics driver is the usual fix; a card which does not support OpenGL 4.6 cannot run this renderer. The process ends with a non-zero exit code.

eu07.ini

Removed options

Old eu07.ini files still load. These entries are read and ignored, with a line in the log:

Entry	What happens now
gfxrenderer legacy, simple or any other value except default, full and experimental	the default renderer is used (eu07.ini: gfxrenderer "X" is no longer supported, using "default")
usevbo	ignored (eu07.ini: "usevbo" is no longer supported and was ignored)
gfx.usegles	ignored, same message
gfx.angleplatform	ignored, same message

gfxrenderer full is still taken for default.

New options

Entry	Default	Meaning
gfx.lights.clustered yes/no	yes	yes: every lit vehicle headlight within 1 km lights the surroundings (see below). no: the shading goes through the first dynamiclights headlights only, as the old renderer did; useful to compare images or to work around a problem
gfx.lights.clusterheatmap yes/no	no	debug view: the number of lights in each cluster, drawn over the image

Sky light and exposure

All of these are optional; a missing entry takes the default. The switches can also be changed while the simulator runs, in the Sky and exposure debug window. With every switch set to no the image is as before these options existed.

Entry	Default	Meaning
gfx.ambient.sh yes/no	yes	the ambient light depends on where a surface faces: more from the bright part of the sky, less from the ground below. The average stays the ambient light the simulation works out
gfx.ambient.sh.strength	1.0	0..2: how much the ambient light differs between directions (0 = uniform, as before)
gfx.ambient.groundalbedo	0.1	0..1: how much light the ground below the horizon gives back (to the directional ambient light and to the atmosphere)
gfx.envmap.ggx yes/no	yes	rough reflections read the environment map prefiltered with the GGX lobe (made in a compute pass after each update of the map) instead of its plain mipmaps
gfx.atmosphere yes/no	yes	the sky, the colour of the sunlight, the ambient light and the fog colour come from a physical model of the atmosphere (Hillaire 2020) during the day; the old sky takes over between 10 degrees of sun elevation and 6 degrees below the horizon, and at night. Render only: the simulation keeps its own values
gfx.atmosphere.sky	1.0	brightness of the drawn sky and of the fog colour (1 = calibrated against the old sky)
gfx.atmosphere.ambient	1.0	brightness of the ambient light from the atmosphere
gfx.atmosphere.sun	1.0	brightness of the sunlight from the atmosphere
gfx.atmosphere.haze	1.0	amount of aerosols on a clear day (whiter, hazier sky); the weather adds to it with the overcast
gfx.atmosphere.altitude	200	height of the scenery above the sea level, metres
gfx.postfx.autoexposure yes/no	yes	the exposure follows the average brightness of the image (luminance histogram, compute pass)
gfx.postfx.autoexposure.key	0.3	average luminance of the image the exposure is set for
gfx.postfx.autoexposure.min	-1.0	the most the exposure darkens a bright image, EV
gfx.postfx.autoexposure.max	0.5	the most the exposure brightens a dark image, EV. Kept low on purpose: tunnels and the night are not meant to be brightened much
gfx.postfx.autoexposure.speed.dark	1.0	rate of adaptation to a darker image, 1/s
gfx.postfx.autoexposure.speed.bright	3.0	rate of adaptation to a brighter image, 1/s
gfx.postfx.autoexposure.compensation	0.0	fixed exposure correction, EV; applies also with the automatic exposure off
gfx.postfx.bloom yes/no	yes	glow around bright parts of the image
gfx.postfx.bloom.intensity	0.04	share of the glow in the image
gfx.postfx.bloom.threshold	0.0	luminance below which nothing glows; 0 = everything contributes a little (physically based)

The automatic exposure and the bloom need the post processing pipeline (gfx.skippipeline no, the default). Model previews of the editor use none of these.

Ambient occlusion

Darkening of creases, corners and the ground under objects, worked out from the depth of the image (screen space) and multiplied into the image before the motion blur and the tonemapping. It works with and without motion blur. It darkens all light alike, the sun and the headlights included; limiting it to the ambient light needs the depth before the shading (a depth prepass), which is planned later.

Entry	Default	Meaning
gfx.postfx.ao gtao/ssao/no	gtao	gtao (or yes): ground truth ambient occlusion (Jimenez et al. 2016), at half the resolution with a depth aware smoothing and upsampling. ssao: the older, experimental ssao. no: none, and no targets are made for it; the mode can then not be turned on in the debug window
gfx.postfx.ao.radius	1.5	0.1..10: reach of the occluders, metres
gfx.postfx.ao.strength	1.0	0..4: power the occlusion is raised to; 1 = as computed, 0 = none
gfx.postfx.ao.bounce	0.3	0..1: albedo of the surfaces assumed for the light that comes back after more bounces (brightens the occlusion a little)
gfx.postfx.ao.quality slices steps	3 4	directions searched around each pixel (1..8) and samples on each side of a direction (1..16)

Changed option

dynamiclights (0..7) used to limit the number of headlight sets that light the surroundings. It is still read, but it only takes effect with gfx.lights.clustered no.

What looks different from the previous renderer

• No limit of 7 lit headlights. All lit headlights within 1 km take part in the lighting (each lit end of a vehicle counts separately), up to 255 in the buffer and 64 reaching any one part of the view. Beyond these capacities the farthest and dimmest lights are dropped, and the statistics show how many.
• Outside the beam texture a headlight adds nothing. Before, the edge of the texture was stretched beyond the beam, which could leave a faint glow around vehicles. This also applies with gfx.lights.clustered no.
• Reflections (environment map) are lit with the sun as seen from the reflection itself, and vehicle headlights no longer light the scene in them.
• Motion blur and ambient occlusion read the real depth of the scene. Before, the depth texture was read in a way the specification leaves undefined, and the result depended on the driver.
• Lines are 1 pixel wide, as they always were on this kind of context. The widths the code asked for (catenary wires, map tracks) never took effect.

The editor (F11, orthographic view), the reflection pass and the model previews do not use clusters. The editor goes through the first dynamiclights headlights, the reflections through the sun only.

Statistics and debugging

• Shift+F12, Gfx Renderer: the lights: row gives the number of lit headlight sets, how many did not fit, and clustered or first N. With clusters on, clusters: (rebuilding of the grid, which happens when the projection or the draw range change) and cull: (assigning lights to clusters, every frame) show the GPU time, and cluster lists: the size of the lists and the number of dropped (cluster, light) pairs (overflow, with its peak). A non-zero overflow means some cluster held more than 64 lights.
• Light clusters window (in debug mode, menu Windows, item Headlight config opens the renderer debug windows): the switch for clustered lights, the heat map, the grid state and the same counters.
• Sky and exposure window (next to the Light clusters window): the switches and scales above, the share of the atmosphere, the colours of the sun, ambient light and fog in use, and the measured luminance and exposure. Shift+F12 shows the GPU time of atmosphere: (look-up tables, only when the sun moved or the weather changed), envmap ggx: (prefiltering, with each update of the environment map), exposure: and bloom:. The same window holds the ambient occlusion mode and its settings; Shift+F12 shows its time as ambient occlusion: (gtao only).
• gfx.gldebug yes turns on the OpenGL debug output (KHR_debug); messages go to the log.

Building

-DWITH_OPENGL_MODERN=ON (default) builds this renderer; WITH_OPENGL_LEGACY and the GLES / ANGLE options are gone. Linux builds still use -DWITH_BETTER_RENDERER=OFF.

All shaders in shaders/ can be checked without a graphics card against GLSL 4.60, compute stage included:

ci_shadervalidator/build.sh
cd ci_shadervalidator && ./validateshaders

It needs g++ with C++20, glslangValidator (Debian/Ubuntu: glslang-tools) and the ref/glm submodule. The same check runs in CI for changes to shaders and the gl/ wrappers.