Notes

You write GLSL source by hand; glCreateShader only gives you an empty GPU container to load it into. One .glsl file = one shader object = one handle.

Files

• name.vert.glsl / name.frag.glsl. The suffix is for humans, not the compiler.
• First line, nothing before it: #version 330 core
• In Qt projects loaded via ":/glsl/...", every shader file must be listed in the .qrc, or the loaded source is empty.

Naming prefixes

Prefix	Meaning	Example
vs_	Vertex shader input from a buffer	in vec3 vs_Pos;
fs_	Vertex output → fragment input	out vec2 fs_Pos; / in vec2 fs_Pos;
u_	Uniform from CPU	uniform float u_Time;
out_	Final fragment output	out vec4 out_Col;

Built-ins

• gl_Position (vert): clip-space output. Must be written, or nothing shows.
• gl_FragCoord (frag): pixel coordinates, origin bottom-left, in pixels.

Writing style

• Write logic for one vertex or one pixel. No loops over the mesh; invocations cannot talk to each other.
• in variables are read-only. Copy to a local to modify.
• ivec.x / ivec.y is integer division. Cast both sides to float.
• Float literals with a dot: 1.0, not 1.
• Swizzle freely: v.xy, c.rgb, vec4(p.xy, 0.0, 1.0).
• Variables declared but unused are removed at compile time, so their location is -1 until the shader uses them.

Vertex shader template (2D, hw04 style)

vec3 p = u_Model * vs_Pos;          // vs_Pos.z = 1 so mat3 translation works
p.x /= aspectRatio;                 // after the model transform
gl_Position = vec4(p.xy, 0.0, 1.0); // z = 0 keeps it inside NDC
fs_Pos = vs_Pos.xy;                 // pattern sticks to the object

Multiple shaders

One program per vert + frag pair, switched with glUseProgram before each draw. One vertex shader can be attached to several programs. Each glCreateShader call makes exactly one shader object.

Related

OpenGL Hub · GLSL in, out and uniform · NDC and aspect ratio correction