[英]OpenGL Ubuntu Depth
I'm writing a simple OpenGL program on Ubuntu which draws two square (one in front of the other) using vertex array. 我正在Ubuntu上编写一个简单的OpenGL程序,它使用顶点数组绘制两个正方形(一个在另一个前面)。 For some reason, the GL_DEPTH_TEST does not seem to work.
由于某些原因,GL_DEPTH_TEST似乎不起作用。 The object in the back appear in front of the one in the front.
后面的对象显示在前面的对象的前面。 Depth buffer is enabled by
深度缓冲区通过以下方式启用
glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_DEPTH);
GL_DEPTH_TEST is enabled by GL_DEPTH_TEST已启用
glEnable(GL_DEPTH_TEST);
and depth buffer is cleared before drawing by 并在绘制之前清除深度缓冲区
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
The complete code is shown below: 完整的代码如下所示:
#define BUFFER_OFFSET( offset ) ((GLvoid*) (offset))
#define NUM_VERTICES 8
vec4 vertices[8] =
{{0.0, 0.0, -0.25, 1.0}, // front
{0.0, 0.5, -0.25, 1.0},
{0.5, 0.5, -0.25, 1.0},
{0.5, 0.0, -0.25, 1.0},
{0.25, 0.25, -0.75, 1.0}, // back
{0.25, 0.75, -0.75, 1.0},
{0.75, 0.75, -0.75, 1.0},
{0.75, 0.25, -0.75, 1.0}};
vec4 vertex_colors[8] =
{{1.0, 0.0, 0.0, 1.0}, // red
{1.0, 0.0, 0.0, 1.0},
{1.0, 0.0, 0.0, 1.0},
{1.0, 0.0, 0.0, 1.0},
{0.0, 1.0, 0.0, 1.0}, // green
{0.0, 1.0, 0.0, 1.0},
{0.0, 1.0, 0.0, 1.0},
{0.0, 1.0, 0.0, 1.0}};
void init(void)
{
GLuint program = initShader("vshader_td.glsl", "fshader_td.glsl");
glUseProgram(program);
GLuint vao;
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
GLuint buffer;
glGenBuffers(1, &buffer);
glBindBuffer(GL_ARRAY_BUFFER, buffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices) + sizeof(vertex_colors), NULL, GL_STATIC_DRAW);
glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(vertices), vertices);
glBufferSubData(GL_ARRAY_BUFFER, sizeof(vertices), sizeof(vertex_colors), vertex_colors);
GLuint vPosition = glGetAttribLocation(program, "vPosition");
glEnableVertexAttribArray(vPosition);
glVertexAttribPointer(vPosition, 4, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
GLuint vColor = glGetAttribLocation(program, "vColor");
glEnableVertexAttribArray(vColor);
glVertexAttribPointer(vColor, 4, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(sizeof(points)));
glEnable(GL_DEPTH_TEST);
glClearColor(1.0, 1.0, 1.0, 1.0);
}
void display(void)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glDrawArrays(GL_QUADS, 0, NUM_VERTICES);
glutSwapBuffers();
}
int main(int argc, char **argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_DEPTH);
glutInitWindowSize(512, 512);
glutCreateWindow("Test Depth");
glewInit();
init();
glutDisplayFunc(display);
glutMainLoop();
return 0;
}
The vertex shader is shown below: #version 130 顶点着色器如下所示:#version 130
in vec4 vPosition;
in vec4 vColor;
out vec4 color;
void main()
{
color = vColor;
gl_Position = vPosition;
}
and the fragment shader is shown below: #version 130 片段着色器如下所示:#version 130
in vec4 color;
out vec4 fColor;
void main()
{
fColor = color;
}
Why object in the front is blocked by the object in the back? 为什么前面的物体被后面的物体阻挡?
In the vertex shader, you do 在顶点着色器中,您可以
in vec4 vPosition; [....] gl_Position = vPosition;
without applying any transformations. 无需进行任何转换。 Since
gl_Position
is the clip space position of the vertex, this means that your vertex coordinates are interpreted as being specified in clip space. 由于
gl_Position
是顶点的裁剪空间位置,因此这意味着您的顶点坐标被解释为在裁剪空间中指定。
And your vertex coordinates 和你的顶点坐标
vec4 vertices[8] = {{0.0, 0.0, -0.25, 1.0}, // front [...] {0.25, 0.25, -0.75, 1.0}, // back
just imply that the points you marked as "front" lie behind the ones you marked as "back". 只是意味着你标记为您标记为“回”的那些背后的 “前”谎言之分。
I don't know how you came to the assumption that it should be the other way round, I can only guess that you confused this with classical, left-handed OpenGL eye space convention where the "camera: looks into -z direction - but that is totally irrelevant here, since you never established an eye space at all, and draw directly in clip space. 我不知道您是如何认为应该相反的,我只能猜测您将其与经典的左手OpenGL眼睛空间约定混淆了,其中“相机:朝-z方向看-这在这里完全无关紧要,因为您根本没有建立眼睛空间,而是直接在剪辑空间中绘制。
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