I would like to be able to set a constant value for one of the vertex attributes in D3D11.
What would be the equivalent of the following code in D3D11?
glVertexAttribPointer(pos, &pos[0], ...);
glEnableVertexAttribArray(pos);
glVertexAttribPointer(color, NULL, ...);
glDisableVertexAttribArray(color);
glVertexAttrib4fv(color, &defaultColor);
glDrawArrays(...);
When creating the input layout for the Input Assembler you can specify if an attribute is provided per vertex or per instance:
typedef enum D3D11_INPUT_CLASSIFICATION {
D3D11_INPUT_PER_VERTEX_DATA = 0,
D3D11_INPUT_PER_INSTANCE_DATA = 1
} D3D11_INPUT_CLASSIFICATION;
You can provide the color that is constant for all vertices on a per instance basis.
Using glVertexAttrib4fv with glDrawArrays means the constant is the same to all vertices in the draw.
Tutorial 7 “Texture Mapping and Constant Buffers” in directx sdk (June 2010) describes a general method of passing constants to a shader.
Related
I'm making a voxel engine and I can render a chunk. I'm using instanced rendering, meaning that I can render all of the chunk with a single draw call. Every blocks of a chunk has a single int (From 0 to 4095) that defines his block type (0 for air, 1 for dirt, etc...). I wanna be able to render my block by applying the good texture in my fragment shader. My chunk contains a tri-dimensionnal array :
uint8_t blocks[16][16][16]
The problem is that I can't find a way to send my array of int to the shader. I tried using a VBO but it makes no-sense (I didn't get any result). I also tried to send my array with glUniform1iv() but I failed.
Is it possible to send an array of int to a shader with glUniformX() ?
In order to prevent storing big data, can I set a byte (uint8_t) instead of int with glUniformX() ?
Is there a good way to send that much data to my shader ?
Is instanced drawing a good way to draw the same model with different textures/types of blocks.
For all purposes and intents, data of this type should be treated like texture data. This doesn't mean literally uploading it as texture data, but rather that that's the frame of thinking you should be using when considering how to transfer it.
Or, in more basic terms: don't try to pass this data as uniform data.
If you have access to OpenGL 4.3+ (which is a reasonably safe bet for most hardware no older than 6-8 years), then Shader Storage Buffers are going to be the most laconic solution:
//GLSL:
layout(std430, binding = 0) buffer terrainData
{
int data[16][16][16];
};
void main() {
int terrainType = data[voxel.x][voxel.y][voxel.z];
//Do whatever
}
//HOST:
struct terrain_data {
int data[16][16][16];
};
//....
terrain_data data = get_terrain_data();
GLuint ssbo;
GLuint binding = 0;//Should be equal to the binding specified in the shader code
glGenBuffers(1, &ssbo);
glBindBuffer(GL_SHADER_STORAGE_BUFFER, ssbo);
glBufferData(GL_SHADER_STORAGE_BUFFER, GLsizeiptr size, data.data, GLenum usage);
glBindBufferBase(GL_SHADER_STORAGE_BUFFER, binding, ssbo);
glBindBuffer(GL_SHADER_STORAGE_BUFFER, 0);
Any point after this where you need to update the data, simply bind ssbo, call glBufferData (or your preferred method for updating buffer data), and then you're good to go.
If you're limited to older hardware, you do have some options, but they quickly get clunky:
You can use Uniform Buffers, which behave very similarly to Shader Storage Buffers, but
Have limited storage space (65kb in most implementations)
Have other restrictions that may or may not be relevant to your use case
You can use textures directly, where you convert the terrain data to floating point values (or use as integers, if the hardware supports integer formats internally), and then convert back inside the shader
Compatible with almost any hardware
But requires extra complexity and calculations in your shader code
I do second the approach as laid out in #Xirema's answer, but come to a slightly different recommendation. Since your original data type is just uint8_t, using an SSBO or UBO directly will require to either waste 3 bytes per element or to manually pack 4 elements into a single uint. From #Xirema's answer:
For all purposes and intents, data of this type should be treated like texture data. This doesn't mean literally uploading it as texture data, but rather that that's the frame of thinking you should be using when considering how to transfer it.
I totally agree to that. Hence I recommend the use of a Texture Buffer Object (TBO), (a.k.a. "Buffer Texture").
Using glTexBuffer() you can basically re-interpret a buffer object as a texture. In your case, you can just pack the uint8_t[16][16][16] array into a buffer and interpret it as GL_R8UI "texture" format, like this:
//GLSL:
uniform usamplerBuffer terrainData;
void main() {
uint terrainType = texelFetch(terrainData, voxel.z * (16*16) + voxel.y * 16 + voxel.x).r
//Do whatever
}
//HOST:
struct terrain_data {
uint8_t data[16][16][16];
};
//....
terrain_data data = get_terrain_data();
GLuint tbo;
GLuint tex;
glGenBuffers(1, &tbo);
glBindBuffer(GL_TEXTURE_BUFFER, tbo);
glBufferData(GL_TEXTURE_BUFFER, sizeof(terrain_data), data.data, usage);
glGenTextures(1, &tex);
glBindTexture(GL_TEXTURE_BUFFER, tex);
glTexBuffer(GL_TEXTURE_BUFFER, GL_R8UI, tbo);
Note that this will not copy the data to some texture object. Accessing the texture means directly accessing the memory of the buffer.
TBOs also have the advantage that they are available since OpenGL 3.1.
I've been writing something using GL3.3 which takes a uniform buffer, and uses the information from it to select sprite tiles in a frag shader. It's working on my desktop, with a Nvidia GTX780, but my AMD based laptop (A6-4455M) has some issues with it. Both are on the latest (or very recent) drivers.
Back to the code, It first of all sets up a uniform buffer, which consists of two uints, and a uint array. They then get filled, and are accessed in the shader. At first I got a GL error on the laptop because I was not allocating enough, but a temporary change taking padding into account has sorted that out, and now data is actually being buffered.
The first two uints are no problem. I've also got the array somewhat readable in the shader, there is just one problem; The data is multiplied by four! At the moment the array is just some test data, initialized to its index, so spriteArr[1] == 1, spriteArr[34] == 34, etc. However, Accessing it in the shader, spriteArr[10] gives 40. This goes all the way up to spriteArr[143] == 572. Beyond this and it's something else. I don't know exactly why this is, but it would appear to be an incorrect offset.
I am using the shared uniform layout, and getting the uniform offsets from GL itself, so they should be correct. I did notice that the offsets on the AMD card are much larger, as if it is adding more padding. They are always 0,4,8 on the desktop, but 0,16,32 on the laptop.
If it makes any difference, there is another UBO (binding point 0), which is used for the view and projection matrices. These work as intended. However it is not used in the fragment shader. It is also created before this UBO.
UBO initialisation code:
GLuint spriteUBO;
glGenBuffers(1, &spriteUBO);
glBindBuffer(GL_UNIFORM_BUFFER, spriteUBO);
unsigned maxsize = (2 + 576 + 24) * sizeof(GLuint);
/*Bad I know, but temporary. AMD's driver adds 24 bytes of padding. Nvidias has none.
Not the cause of this problem. At least ensures we have enough allocated. */
glBufferData(GL_UNIFORM_BUFFER, maxsize, NULL, GL_STATIC_DRAW);
glBindBuffer(GL_UNIFORM_BUFFER, 0);
//Set binding point
GLuint spriteUBOIndex = glGetUniformBlockIndex(programID, "SpriteMatchData");
glUniformBlockBinding(programID, spriteUBOIndex, 1);
static const GLchar *unames[] =
{
"width", "height",
//"size",
"spriteArr"
};
GLuint uindices[3];
GLint offsets[3];
glGetUniformIndices(programID,3,unames,uindices);
glGetActiveUniformsiv(programID, 3, uindices, GL_UNIFORM_OFFSET, offsets);
//buffer stuff
glBindBufferBase(GL_UNIFORM_BUFFER, 1, spriteUBO);
glBufferSubData(GL_UNIFORM_BUFFER,offsets[0], sizeof(GLuint), tm.getWidth());
glBufferSubData(GL_UNIFORM_BUFFER, offsets[1], sizeof(GLuint), tm.getHeight());
glBufferSubData(GL_UNIFORM_BUFFER, offsets[2], tm.getTileCount() * sizeof(GLuint), tm.getSpriteArray());
Fragment Shader:
layout (shared) uniform SpriteMatchData{
uint width, height;
uint spriteArr[576];};
Then later on I experiment with the array with something like this:
if(spriteArr[10] == uint(40))
{
debug_colour = vec4(0.0,1.0,0.0,0.0);//green
}
else
{
debug_colour = vec4(1.0,0.0,0.0,0.0); //red
}
With debug_colour turning green in this instance.
Is there any way to sort this out with something that works with both systems? Why is the AMD driver handling this so differently? Could it be a bug in the way it deals with uniform uint arrays?
Why is the AMD driver handling this so differently?
Because that's what you asked for:
layout (shared) uniform SpriteMatchData
You explicitly asked for shared layout. That layout is implementation defined. Therefore, two different implementations are allowed to give you two different layouts. As such, if you want to use SpriteMatchData in a platform-independent way, you must query its layout from the program after linking it.
While you did query the offsets for the values, you did not query the array stride: the byte offset from element to element within the array. There is nothing in the specification that requires that shared layouts tightly pack arrays.
Really though, there's pretty much no reason not to use std140 layout. You can avoid all of this querying of offsets and simply design C++ structs that can be directly consumed by GLSL.
I have some Cg Vertex shader and want to get the compiled binary from it to cache.
The way I load the Cg vertex is using glProgramStringARB, the problem with that is that I can't retrieve any value from glGetProgramiv and glGetProgramBinary.
Here is a example code of what I'm doing:
CGprogram program = cgCreateProgram(context, CG_SOURCE, source, ...);
const char* programARB = static_cast<char*>(cgGetProgramString(program,
CG_COMPILED_PROGRAM));
GLuint id;
glGenProgramsARB(1, id);
glBindProgramARB(GL_VERTEX_PROGRAM_ARB, id);
glProgramStringARB(GL_VERTEX_PROGRAM_ARB, GL_PROGRAM_FORMAT_ASCII_ARB,
static_cast<GLsizei>(strlen(programARB)), programARB);
GLint length = -10;
glGetProgramiv(GL_VERTEX_PROGRAM_ARB, GL_PROGRAM_BINARY_LENGTH, &lenght);
printf("LENGTH: %d\n", length);
I initialized length with -10 just to see if the variable would change with glGetProgramiv call, but I always get the -10 as result.
the problem with that is that I can't retrieve any value from glGetProgramiv and glGetProgramBinary.
Of course you can't. You're confusing ARB_vertex_program with GLSL programs. They're not the same thing.
glGetProgramiv takes a GLSL program object (among other things). Odds are good that OpenGL is giving you a GL_INVALID_VALUE error, since the first argument is almost certainly not a valid program object created by glCreateProgram.
You can't get a program binary for an ARB_vertex_program. You would need to compile your Cg shader to GLSL, then use the standard GLSL compile/link process, and get the binary from that.
Why are there mismatching types in OpenGL?
For example, if I have a vertex buffer object,
GLuint handle = 0;
glGenBuffers(1, &handle_); // this function takes (GLsizei, GLuint*)
Now if I want to know the currently bound buffer
glGetIntegerv( GL_ARRAY_BUFFER_BINDING, reinterpret_cast<GLint *>(&handle ) ); // ouch, type mismatch
Why not have a glGetUnsignedIntegerv or
have glGenBuffers take an GLint * instead.
That is because glGetIntegerv function is intended to get any integral type of information back from OpenGL. It includes also GLint type values (negative ones). And also it includes multiple component values like GL_VIEWPORT:
GLint viewport[4];
glGetIntegerv(GL_VIEWPORT, viewport);
From one point of view - it is simpler to have just one function for getting values back, instead of hundreds for each specific parameter.
Form other point of view - of course it's a bit ugly to cast types.
But no idea why they didn't use GLint for buffer id.
Anyway - you shouldn't bee calling any glGet... functions. They are slow and often requires waiting on GPU complete previous commands - meaning CPU will wait idle in that time.
There is a bool type for shader variables I'd like to use, but I couldn't find what size it have. This matters because when setting up vertex attribute pointer I specify the type of data which can be
GL_BYTE,
GL_UNSIGNED_BYTE,
GL_SHORT,
GL_UNSIGNED_SHORT,
GL_INT,
GL_UNSIGNED_INT,
GL_FLOAT, or
GL_DOUBLE
In c++ generally bool should have the same size as 4 byte int, but can I assume the same for GLSL or does it have only 1 byte?
This matters because when setting up vertex attribute pointer I specify the type of data which can be
It's irrelevant, since vertex attributes cannot be booleans. From the GLSL 3.30 specification:
Vertex shader inputs can only be float, floating-point vectors, matrices, signed and unsigned integers and integer vectors. Vertex shader inputs can also form arrays of these types, but not structures.
Booleans are not on that list.
However, if you want to know what the size of a GLSL bool is in terms of uniform blocks, it has the same size as uint: 32-bits.