Shader – OpenGL easy ways to make money Wiki

• fragment shaders: once per fragment generated by the rasterizer. It may be executed more than this, as "helper" fragment shader instances may be used by the implementation. These instances however cannot write data (in any way, whether fragment shader outputs, image load store or anything else). They exist mostly to compute implicit derivatives to make many easy ways to make money texture sampling functions work.

The command processor is responsible for reading a command and easy ways to make money telling the mathematical unit what to do, then reading the next command. If that command is a branch operation, it is the command processor that figures out where to easy ways to make money branch to, to pick which command to execute next. For conditional branches, the command can be broken down into the math that easy ways to make money computes the condition (executed on the math unit), followed by the command processor reading the result of the easy ways to make money condition and picking the next command to execute based on easy ways to make money that.

However, let’s alter our scenario. What if all of the above command sequences were actually easy ways to make money the same sequence of commands, simply acting on different input values and writing to different easy ways to make money output locations? If we were to design a processor for such an easy ways to make money operation, it could have a single command processor which feeds multiple easy ways to make money mathematical units. It reads one command, and tells the math units to execute that command on easy ways to make money that units own variables. Each math unit has its own temporary values as well, to serve as intermediates.

This all works… Right up until you need to execute a conditional branch easy ways to make money ( if, for, etc). What happens if the math computations that lead to a easy ways to make money conditional branch result in different values for different command sequences? The desired result would be that these sequences would execute easy ways to make money different commands. But we only have one command processor, so it can’t pick different commands to execute. How do you deal with this?

When a conditional branch diverges like this, you have to do something unpleasant. The branch can be broken down into path A and easy ways to make money path B. The command processor basically has to freeze all of the easy ways to make money math units that need to execute path B commands. Then it executes the path A commands. Once that’s done, it goes back to the branch and execute path B’s commands.

What happens in real gpus is that you have one easy ways to make money "mathematical unit" which can perform the same action on multiple pieces of easy ways to make money input data, writing to multiple intermediate data locations. That is, if you want to do x = 2 + 3 and y = 6 + 9, you’re conceptually executing the same command: addition. So what a GPU does is bundle them together. You’re not doing two separate addition commands; you’re doing (x, y) = (2, 3) + (6, 9) as a single operation.

Note that this is different from dynamically uniform expressions. All statically uniform expressions are dynamically uniform too, but not vice-versa. If a non-statically uniform value happens to be constant throughout a shader easy ways to make money operation (all shader invocations get the same input value, for example), then expressions based on that value are dynamically uniform. But because the compiler cannot know this, it must assume that divergence is possible.

Even with potentially divergent branches, compilers attempt to avoid the pain of true execution divergence easy ways to make money wherever possible. For example, a simple ? : expression will rarely cause SIMD divergence; the compiler will usually generate code that evaluates *both expressions*, and each individual invocation will discard one or the other easy ways to make money based on the condition. If those expressions involve calling complex functions, the compiler may allow true divergence, but if it’s simple math like value = condition ? X + 5 : Y – 20, the compiler will almost certainly execute both.

Shaders have access to a wide variety of resources. They can access textures, uniforms, uniform blocks, image variables, atomic counters, shader storage buffers, and potentially other information. There are limits however on exactly how much stuff each easy ways to make money shader stage can access. Each resource has a query-able maximum count of accessible resources for each stage.

The query-able limits, and their associated meanings, are as follows. Note that the "*" is the stage name. It can be VERTEX, TESS_CONTROL, TESS_EVALUATION, COMPUTE, GEOMETRY or FRAGMENT. These values also have an opengl-required minimum; opengl implementations (of a certain version) will support at least this many of that resource. MAX_*_UNIFORM_COMPONENTS this is the number of active components of uniform easy ways to make money variables that can be defined outside of a uniform block. The term "component" is meant as the basic component of a vector/matrix. So a vec3 takes up 3 components. The minimum value here is 1024, enough room for 256 vec4s. GL_MAX_*_UNIFORM_BLOCKS the maximum number of uniform blocks that this shader easy ways to make money stage can access. The opengl-required minimum is 12 in GL 3.3, and 14 in GL 4.3. GL_MAX_*_INPUT_COMPONENTS the maximum number of components that this stage can easy ways to make money take as input. The required minimum value differs from shader stage to shader easy ways to make money stage. Note that vertex shaders do not have this value, as they use a different input mechanic based on vertex easy ways to make money attributes. Their limit is GL_MAX_VERTEX_ATTRIBUTES, where each attribute can be at most 4 components. GL_MAX_*_OUTPUT_COMPONENTS the maximum number of components that this stage can easy ways to make money output. The required minimum value differs from shader stage to shader easy ways to make money stage. Note that fragment shaders do not have this value, as they use a different output mechanic based on draw easy ways to make money buffers. Their limit is GL_MAX_DRAW_BUFFERS, where each draw buffer output can be at most 4 easy ways to make money components. GL_MAX_*_TEXTURE_IMAGE_UNITS the maximum number of texture image units that the easy ways to make money sampler in this shader can access. The opengl-required minimum value is 16 for each stage.

Note: for legacy reasons, the enumerator for the fragment shader equivalent is called GL_MAX_TEXTURE_IMAGE_UNITS. No " FRAGMENT". GL_MAX_*_IMAGE_UNIFORMS (requires GL 4.2/ arb_shader_image_load_store) the maximum number of image variables for this shader stage. The opengl-required minimum is 8 for fragment and compute shaders, and 0 for the rest. This means implementations may not allow you to use image easy ways to make money variables in non-fragment or compute stages. GL_MAX_*_ATOMIC_COUNTERS (requires GL 4.2/ arb_shader_atomic_counters) the maximum number of atomic counter variables that this stage easy ways to make money can define. The opengl-required minimum is 8 for fragment and compute shaders, and 0 for the rest. GL_MAX_*_ATOMIC_COUNTER_BUFFERS (requires GL 4.2/ arb_shader_atomic_counters) the maximum number of different buffers that the atomic counter easy ways to make money variables can come from. The opengl-required minimum is 1 for fragment shaders, 8 for compute shaders (note: possible spec typo), and again 0 for the rest. GL_MAX_*_SHADER_STORAGE_BLOCKS (requires GL 4.3/ arb_shader_storage_buffer_object) the maximum number of different shader storage blocks that a easy ways to make money stage can use. For fragment and compute shaders, the opengl-required minimum is 8; for the rest, it is 0. Aggregate limits

While these define the resources usable to a shader stage, there are some limits beyond this, which cover all shader stages in total. GL_MAX_UNIFORM_BUFFER_BINDINGS the limit on the number of uniform buffer binding easy ways to make money points. This is the limit for glbindbufferrange when using GL_UNIFORM_BUFFER. In GL 3.3, this value is a minimum of 36 (3 shader stages, with a minimum of 12 blocks per stage). In 4.3, this value is a minimum of 72. GL_MAX_COMBINED_UNIFORM_BLOCKS the maximum number of uniform blocks that all of easy ways to make money the active programs can use. If two (or more) shader stages use the same block, they count separately towards this limit. In GL 3.3, this was 36; in 4.3, it is 70. GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS the total number of texture units that can be easy ways to make money used from all active programs. This is the limit on glactivetexture(GL_TEXTURE0 + i) and glbindsampler. In GL 3.3, this was 48; in 4.3, it is 96. GL_MAX_TRANSFORM_FEEDBACK_SEPARATE_ATTRIBS when doing separate mode transform feedback, this is the maximum number of varying variables that can easy ways to make money be captured. This has a minimum of 4. GL_MAX_TRANSFORM_FEEDBACK_SEPARATE_COMPONENTS when doing separate mode transform feedback, this is the maximum number of components for a single easy ways to make money varying variable (note that varyings can be arrays or structs) that can be captured. This has a minimum of 4. GL_MAX_TRANSFORM_FEEDBACK_INTERLEAVED_COMPONENTS when doing interleaved transform feedback, this is the total number of components that can be easy ways to make money captured within a single buffer. This has a minimum of 64. GL_MAX_TRANSFORM_FEEDBACK_BUFFERS (requires GL 4.0/ arb_transform_feedback3) the maximum number of buffers that can be written to easy ways to make money in transform feedback operations. This has a minimum of 4. GL_MAX_ATOMIC_COUNTER_BUFFER_BINDINGS (requires GL 4.2/ arb_shader_atomic_counters) the total number of atomic counter buffer binding points. This is the limit for glbindbufferrange when using GL_ATOMIC_COUNTER_BUFFER. This value has a minimum of 1. GL_MAX_COMBINED_ATOMIC_COUNTER_BUFFERS (requires GL 4.2/ arb_shader_atomic_counters) the maximum number of atomic counter buffers variables across all easy ways to make money active programs. This value has a minimum of 1. GL_MAX_COMBINED_ATOMIC_COUNTERS (requires GL 4.2/ arb_shader_atomic_counters) the maximum number of atomic counter variables across all active easy ways to make money programs. This value has a minimum of 8. GL_MAX_SHADER_STORAGE_BUFFER_BINDINGS (requires GL 4.2/ arb_shader_atomic_counters) the total number of shader storage buffer binding points. This is the limit for glbindbufferrange when using GL_SHADER_STORAGE_BUFFER. This value has a minimum of 8. GL_MAX_COMBINED_SHADER_STORAGE_BLOCKS (requires GL 4.3/ arb_shader_storage_buffer_object) the maximum number of shader storage blocks across all active easy ways to make money programs. As with ubos, blocks that are the same between stages are counted for easy ways to make money each stage. This value has a minimum of 8. GL_MAX_IMAGE_UNITS (requires GL 4.2/ arb_image_load_store) the total number of image units that can be used easy ways to make money for image variables from all active programs. This is the limit on glbindimagetexture. This value has a minimum of 8. GL_MAX_COMBINED_SHADER_OUTPUT_RESOURCES (requires GL 4.3/ arb_shader_storage_buffer_object) the total number of shader storage blocks, image variables, and fragment shader outputs across all active programs cannot exceed easy ways to make money this number. This is the "amount of stuff" that a sequence of shaders can write to (barring transform feedback). This value has a minimum of 8.

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