3.1 Hello_triangle_pt1.md

• opengl -> 3d space
• screen -> 2d surface pixels
• 3d coordinates ->2d pixels transformation MANAGED BY graphics pipeline
• graphics pipeline : does transformation of
  • 3d space to 2d
  • 2d coords to actual pixels

steps

1 we need triangle data

• 3 points in 3d space
• lets create vertices array having these 3 point's coordinates in main.cpp

2 load the data to gpu

but how?

• we need to create a buffer in gpu memory

   glGenBuffers(1 , &VBO);
  

• load vertex data to gpu buffer

	//bind vbo to curr context
	glBindBuffer(GL_ARRAY_BUFFER,VBO); 
	
	//adding data to context == adding data to VBO 
	glBufferData(
	GL_ARRAY_BUFFER , 
	sizeof(vertices) ,
	vertices ,
	GL_STATIC_DRAW
	);

• need to tell gpu's program how to use this buffer. how?
• create vertex attribute pointer

glVertexAttribPointer(0,3,GL_FLOAT , GL_FALSE , 3 * sizeof(GLfloat) , 0);
glEnableVertexAttribArray(0);

• From the buffer ,this takes every "3" "float" values with "no rescaling" and 3*size(float) bytes offset b/w consecutive attributes and gives to graphics pipeline at index "0" i.e layout (location = 0)

1.3 make Graphics pipeline so that gpu knows what to do with the data

• make vertex shader
  • in our case , vertex attributes at index = 0 is simply forwarded further
  • input : vec3
  • output : gl_Position which is vec4
  • gl_Position if sent down the pipeline

#version 330 core
layout (location = 0) in vec3 aPos;
void main(){
  gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);
  }

• make fragment shader
  • output : FragColor which renders to screen!

#version 330 core
out vec4 FragColor;
void main(){
 FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);
 }

• compile these shaders
• create shader program (i.e link shaders and make pipeline)
• hooray! our graphics pipeline is ready!

[!error] creating triangle only with VBO without VAO seems like not possible on mac with core profile link