OpenGL 工作着色器？

Question

有两个着色器，顶点和片段

const char *vShaderstr = 
"#version 300 es\n"
"layout(location = 0) in vec4 a_color;\n"
"layout(location = 1) in vec2 a_position;\n"
"out vec4 v_color;\n"
"void main()\n"
"{\n"
" v_color = a_color;\n"
" gl_Position.xy = a_position;\n"
" gl_Position.z = 0.0;\n"
" gl_Position.w = 1.0;\n"
"}";
const char *fShaderstr =
    "#version 300 es\n"
    "precision lowp float;\n"
    "in vec4 v_color;\n"
    "out vec4 o_fragColor;\n"
    "void main()\n"
    "{\n"
    " o_fragColor = v_color;\n"
    "}";

问题是我的颜色不是浮点数，而是无符号字节数。并在 int 中定位，而不是在 float 中。当我在花车上沉思时，vec。为了将数据发送到管道，我使用了这样的命令。

glVertexAttribPointer ( 0, 4, GL_UNSIGNED_BYTE, GL_FALSE, 0, pixels );
glVertexAttribPointer ( 1, 2, GL_INT, GL_FALSE, 0, vertices );
glEnableVertexAttribArray ( 0 );
glEnableVertexAttribArray ( 1 );
glDrawArrays ( GL_POINTS, 0, max_draw );

来自字节的像素。 int.

的顶点

Answer 1

请参阅 OpneGL ES glVertexAttribPointer 的 Khronos 组参考页面：

For glVertexAttribPointer, if normalized is set to GL_TRUE, it indicates that values stored in an integer format are to be mapped to the range [-1,1] (for signed values) or [0,1] (for unsigned values) when they are accessed and converted to floating point. Otherwise, values will be converted to floats directly without normalization.

For glVertexAttribIPointer, only the integer types GL_BYTE, GL_UNSIGNED_BYTE, GL_SHORT, GL_UNSIGNED_SHORT, GL_INT, GL_UNSIGNED_INT are accepted. Values are always left as integer values.

您必须将 RGB 颜色的颜色通道从范围 [0, 255] 转换为 [0.0, 1.0]。所以你必须使用：

// normalized = GL_TRUE: [0, 255] -> [0.0, 1.0]
glVertexAttribPointer( 0, 4, GL_UNSIGNED_BYTE, GL_TRUE, 0, pixels );

但是您想按原样使用顶点坐标作为积分坐标。所以你必须使用 glVertexAttribIPointer（关注 I）：

// glVertexAttribIPointer because of integer coordinates
glVertexAttribIPointer( 1, 2, GL_INT, 0, vertices );

顶点着色器中顶点属性的类型必须从vec2更改为ivec2，因为坐标的数据类型是GL_INT:

#version 300 es

layout(location = 0) in vec4 a_color;
layout(location = 1) in ivec2 a_position; // <---- ivec2

out vec4 v_color;

uniform mat4 u_projection;

void main()
{
    v_color = a_color;
    vec2 p = vec2(a_position); // <---- convert from int to float
    gl_Position = u_projection * vec4( p.xy, 0.0, 1.0 );
}

进一步注意，gl_Position 是剪辑 space 坐标通过除以 w 分量转换为标准化设备坐标 (NDC)。在标准化设备 space 中，左下角位于 (-1.0, -1.0)，右上角位于 (1.0, 1.0)。然后将标准化的设备坐标线性映射到 Window 坐标（由 glViewport 设置的视口）。

您必须设置一个投影矩阵，它将顶点坐标转换为剪辑 space（最后归一化设备 space）。

下面的例子设置了一个正交投影矩阵，投影屏幕space坐标，其中左上角为(0,0) 右下角是 (width, height):

GLuint shader_prog = .... ; // shader program object
float  width       = .... ; // viewport width in pixel
float  height      = .... ; // viewport height in pixel

float prj_mat[] = 
{
     2.0f/width,  0.0f,         0.0f,  0.0f,
     0.0f,       -2.0f/height,  0.0f,  0.0f,
     0.0f,        0.0f,        -1.0f,  0.0f,
    -1.0f,        1.0f,         0.0f,  1.0f
};

glLinkProgram( shader_prog );
GLint prj_loc = glGetUniformLocation( shader_prog, "u_projection" );

glUseProgram( shader_prog );
glUniformMatrix4fv( prj_loc, 1, GL_FALSE, prj_mat );

OpenGL 工作着色器？

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