I want to draw a selected number of instances using glDrawElements... but I don't know which function to use and how to set the parameters.
I set the gl_InstanceID in shader and set the shader data through SSBO:
glGenBuffers(1, &SSBO); glBindBuffer(GL_SHADER_STORAGE_BUFFER, SSBO); glBufferData(GL_SHADER_STORAGE_BUFFER, data_vector.size() * sizeof(data_type), data_vector.data(), GL_DYNAMIC_DRAW); glBindBufferBase(GL_SHADER_STORAGE_BUFFER, binding_index, SSBO); I have an array drawable_vector contains bool to check if the vertex is drawn or not.
for(auto index = 0; index < drawable_vector.size(); index ++){ glDrawElements...(???) } I want to draw instance with ID gl_instanceID only when the drawable_vector[index] is true. The size of drawable_vector, data_vector and number of instances are the same.
Edit: Setup & render code
Setup:
//VAO glGenVertexArrays(1, &VAO); glBindVertexArray(VAO); //VBO1 - Position glGenBuffers(1, &VBO1); glBindBuffer(GL_ARRAY_BUFFER, VBO1); glBufferData(GL_ARRAY_BUFFER, 3*sizeof(glm::vec4), vertices.data(), GL_DYNAMIC_DRAW); //VBO2 - color glGenBuffers(1, &VBO2); glBindBuffer(GL_ARRAY_BUFFER, VBO2); glBufferData(GL_ARRAY_BUFFER, 3*sizeof(glm::vec4), colors.data(), GL_DYNAMIC_DRAW); //EBO glGenBuffers(1, &EBO); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO); glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_DYNAMIC_DRAW); //SSBO - models in shader glGenBuffers(1, &SSBO); glBindBuffer(GL_SHADER_STORAGE_BUFFER, SSBO); glBufferData(GL_SHADER_STORAGE_BUFFER, models.size() * sizeof(glm::vec4), models.data(), GL_DYNAMIC_DRAW); glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 2, SSBO); //Set data of shader //in_pos glBindBuffer(GL_ARRAY_BUFFER, VBO1); glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 0, (void *) 0); glEnableVertexAttribArray(0); //in_color glBindBuffer(GL_ARRAY_BUFFER, VBO2); glVertexAttribPointer(1, 4, GL_FLOAT, GL_FALSE, 0, (void *) 0); glEnableVertexAttribArray(1); glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 0, 0); glMemoryBarrier(GL_SHADER_STORAGE_BARRIER_BIT); glBindVertexArray(0); Shader:
#version 450 core out vec4 frag_color; in vec4 out_color; void main() { frag_color = out_color; } #version 430 core layout (location = 0) in vec4 in_pos; layout (location = 1) in vec4 in_color; layout(std430, binding = 2) buffer DataBuffer { mat4 in_models[]; } buffer_data; uniform mat4 view; uniform mat4 projection; out vec4 out_color; void main() { out_color = in_color; gl_Position = projection * view * buffer_data.in_models[gl_InstanceID] * in_pos; } Render:
use_shader(); shader_set_view("view", view); shader_set_projection("projection", projection); update_models(); glBindVertexArray(VAO); glBindBuffer(GL_ARRAY_BUFFER, VBO1); glBindBuffer(GL_ARRAY_BUFFER, VBO2); glBindBuffer(GL_ARRAY_BUFFER, EBO); glBindBuffer(GL_SHADER_STORAGE_BUFFER, SSBO); glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 2, SSBO[0]); glDrawArraysInstanced(GL_TRIANGLES, 0, 3, n_instances); glfwSwapBuffers(window); glBindVertexArray(0); 