Graphics Reference
In-Depth Information
language; in Chapter 8, “Vertex Shaders,” we specifically cover how to
write vertex shaders.
The fragment shader in the example is simple:
char fShaderStr[] =
"#version 300 es \n"
"precision mediump float; \n"
"out vec4 fragColor; \n"
"void main() \n"
"{ \n"
" fragColor = vec4 ( 1.0, 0.0, 0.0, 1.0 ); \n"
"} \n";
Just as in the vertex shader, the first line of the fragment shader declares
the shader version. The next statement in the fragment shader declares
the default precision for float variables in the shader. For more details
on this topic, please see the section on precision qualifiers in Chapter 5,
“OpenGL ES Shading Language.” The fragment shader declares a single
output variable
fragColor
, which is a vector of four components. The
value written to this variable is what will be written out into the color
buffer. In this case, the shader outputs a red color (1.0, 0.0, 0.0, 1.0) for
all fragments. The details of developing fragment shaders are covered in
Chapter 9, “Texturing,” and Chapter 10, “Fragment Shaders.” Again, here
we are just showing you what a fragment shader looks like.
Typically, a game or application would not place shader source strings
inline in the way we have done in this example. In most real-world
applications, the shader is loaded from some sort of text or data file and
then loaded to the API. However, for simplicity and to make the example
program self-contained, we provide the shader source strings directly in
the program code.
Now that we have the shader source code defined, we can go about loading
the shaders to OpenGL ES. The
LoadShader
function in the Hello Triangle
example is responsible for loading the shader source code, compiling it,
and checking it for errors. It returns a
shader object,
which is an OpenGL
ES 3.0 object that can later be used for attachment to a
program object
(these two objects are detailed in Chapter 4, “Shaders and Programs”).
Let's look at how the
LoadShader
function works. First,
glCreateShader
creates a new shader object of the type specified.
