Multiple inputs for Compute shader Open GL ES

Question

I want to create a program that takes multiple vectors and returns one vector in Open GL ES.

I have used the example to write my own code.

If I have following code:

static const char COMPUTE_SHADER[] =
    "#version 310 es\n"
    "layout(local_size_x = 128) in;\n"
    "layout(std430) buffer;\n"
    "layout(binding = 0) buffer Output {\n"
    "uint elements[];\n"
    "} output_data;\n"
    "void main()\n"
    "{\n"
    "    uint ident = gl_GlobalInvocationID.x;\n"
    "output_data.elements[ident] = output_data.elements[ident] * "
    "output_data.elements[ident];\n"
    "}";

...

  GLuint data_buffer;
  glGenBuffers(1, &data_buffer);
  glBindBuffer(GL_SHADER_STORAGE_BUFFER, data_buffer);
  glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 0, data_buffer);
  glBufferData(GL_SHADER_STORAGE_BUFFER, sizeof(GLuint) * 10, (void*)data,
               GL_DYNAMIC_READ);
  GLuint program = glCreateProgram();
  GLuint shader = LoadShader(COMPUTE_SHADER);
  glAttachShader(program, shader);

  glLinkProgram(program);
  glUseProgram(program);

  glDispatchCompute(10, 1, 1);

  std::vector<uint32_t> ready_data(10);

  GLuint* ptr = (GLuint*)glMapBufferRange(GL_SHADER_STORAGE_BUFFER, 0,
                                          sizeof(GLuint) * 10, GL_MAP_READ_BIT);
  std::copy(ptr, ptr + 10, ready_data.begin());
  glUnmapBuffer(GL_SHADER_STORAGE_BUFFER);

it works perfectly fine and stores all I need in the output vector.

But then I want to follow the example and make separate input and output. And it doesn't work:

static const char COMPUTE_SHADER[] =
"   #version 310 es"
"layout(local_size_x = 128) in;"
"layout(std430) buffer;"
"layout(binding = 0) buffer Output {"
"    uint elements[];"
"} output_data;"
"layout(binding = 1) buffer Input0 {"
"    uint elements[];"
"} input_data0;"
"layout(binding = 2) readonly buffer Input1 {"
"uint elements[];"
"} input_data1;"
"void main()"
"{"
"    uint ident = gl_GlobalInvocationID.x;"
"    output_data.elements[ident] = input_data0.elements[ident] * input_data1.elements[ident];"
"}";

uint32_t data1[10] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
  uint32_t data2[10] = {10, 20, 30, 40, 50, 60, 70, 80, 90, 100};
  uint32_t data3[10] = {11, 21, 31, 41, 51, 61, 71, 81, 91, 101};

glGenBuffers(1, &input_buffer1);
  glBindBuffer(GL_SHADER_STORAGE_BUFFER, input_buffer1);
  glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 1, input_buffer1);
  glBufferData(GL_SHADER_STORAGE_BUFFER, sizeof(GLuint) * 10, (void*)data2,
               GL_STREAM_COPY);

  glGenBuffers(1, &input_buffer2);
  glBindBuffer(GL_SHADER_STORAGE_BUFFER, input_buffer2);
  glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 2, input_buffer2);
  glBufferData(GL_SHADER_STORAGE_BUFFER, sizeof(GLuint) * 10, (void*)data3,
               GL_STREAM_COPY);

  glGenBuffers(1, &data_buffer);
  glBindBuffer(GL_SHADER_STORAGE_BUFFER, data_buffer);
  glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 0, data_buffer);
  glBufferData(GL_SHADER_STORAGE_BUFFER, sizeof(GLuint) * 10, (void*)data1,
               GL_DYNAMIC_READ);

  GLuint program = glCreateProgram();
  GLuint shader = LoadShader(COMPUTE_SHADER);
  glAttachShader(program, shader);

  glLinkProgram(program);
  glUseProgram(program);

  glDispatchCompute(10, 1, 1);

GLuint* ptr = (GLuint*)glMapBufferRange(GL_SHADER_STORAGE_BUFFER, 0,
                                          sizeof(GLuint) * 10, GL_MAP_READ_BIT);
  std::copy(ptr, ptr + 10, ready_data.begin());
  glUnmapBuffer(GL_SHADER_STORAGE_BUFFER);

It outputs just numbers 1 2 3 .. 10 while I expect them multiplied elementwise.

score 0 · Accepted Answer · answered Jul 16 '18 at 19:00

The 2nd compute shader doesn't even compile, because of a missing newline.

The first 2 lines of the compute shader

static const char COMPUTE_SHADER[] =
"   #version 310 es"
"layout(local_size_x = 128) in;"
.....

result in

   #version 310 eslayout(local_size_x = 128) in;

Add a newline at the end of the first line to solve the issue:

static const char COMPUTE_SHADER[] =
"#version 310 es\n"
"layout(local_size_x = 128) in;"
.....

But I recommned to use Raw string literals (C++11):

static const char COMPUTE_SHADER[] = R"(
#version 310 es

layout(local_size_x = 128) in;
layout(std430) buffer;

layout(binding = 0) buffer Output {
    uint elements[];
} output_data;

layout(binding = 1) buffer Input0 {
    uint elements[];
} input_data0;

layout(binding = 2) readonly buffer Input1 {
    uint elements[];
} input_data1;

void main()
{
    uint ident = gl_GlobalInvocationID.x;
    output_data.elements[ident] = input_data0.elements[ident] * input_data1.elements[ident];
}
)";

It turned out that it was not only error in the shader, but in the end solving these errors made code work — sooobus, Jul 17 '18 at 11:32

Multiple inputs for Compute shader Open GL ES

1 Answers1