OpenGLRenderer

Advanced OpenGL

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• Advanced OpenGL
  • Advanced Datas
    • Buffer Subdata
    • Batching Vertex Attributes
    • Copying Buffers
  • Advanced GLSL
    • Built In Variables
    • Interface Blocks
    • Uniform Buffer Objects

Advanced Datas

Buffer Subdata

• Buffer content is target dependant. Binded to GL_ARRAY_BUFFER it means vertices, but something else when binded elsewhere.
• GLBufferSubData can be use to fill parts of a pre-allocated buffer.

  glMapBuffer(GL_ARRAYBUFFER, GL_WRITE_ONLY); // return a void* to buffer adress memory. (Usefull to load from file to GPU without stocking in temp memory)
  

  memcpy(ptr, data, sizeof(data)); // -- copy the data and then
  GlUnmapBuffer(); // unmap the pointer.
  

Batching Vertex Attributes

• Insted of interleaving data in VAO like pos,normal,texcoord, 123123123 etc we can do 11122233 using SubData.
• Remplacer l’implémentation d’assimp par des subdata dans le VAO ? - Well, no, because interleaved it more optimal when reading vertex attributes in vertex shader

Copying Buffers

// -- Prototype
void  glCopyBufferSubData(GLenum readtarget, GLenum writetarget, GLintptr readoffset, GLintptr writeoffset, GLsizeptr size);
// -- You can bind to two specials buffers : copy and read buffer
glBindBuffer(GL_COPY_READ_BUFFER, vbo1);
glBindBuffer(GL_COPY_WRITE_BUFFER, vbo2);
// -- Then this read from vbo1 with 0 offset and copy to vbo2 with 0, 8 * sizeof(float) datas !
glCopyBufferSubData(GL_COPY_READ_BUFFER, GL_COPY_WRITE_BUFFER, 0, 0, 8 * sizeof(float));

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Advanced GLSL

• Built-in variables
• News way of organizing shaders inputs/outputs
• Uniform Buffer Objects (UBO)

Built In Variables

// Vertex
gl_Position // output vector of vertex shader
gl_PointSize //influence point size when glEnable(GL_PROGRAM_POINT_SIZE); Fun and usefull for particles
gl_VertexID // Current vertex ID (Was usefull in Veritasium grass video)

// Fragment
gl_FragColor // output color
gl_FragCoord // fragment coord : Z value = depth // x/y = Screen Space Coordinates !
gl_FrontFacing // true or false if facing use - Create Curses

Interface Blocks

• Allows in and out block, similar to structs
• Elements inside the block MUST be in the same order in differents shaders stage.

Uniform Buffer Objects

• Later. [TODO]
• Advanced GLSL : Finish last part with UBO for shader refactoring !
• Gemotry Shaders : Apres UBO, à l’air cool pour Drawline on the fly though (Visualize Normals)
• Instancing : Ok to do when you want to start particles
• Anti Aliasing : Pas needed dessuite, quand on voudra

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