Notes for OpenGL - 3

最新推荐文章于 2024-05-19 09:31:32 发布

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#filter #textures #components #distance #border #image

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本文介绍如何使用OpenGL绘制一个简单的四面体，并探讨了视距与对象大小的关系。此外，还详细解释了纹理映射的过程，包括生成、绑定纹理及设置纹理参数等关键步骤。

1. 今天做了一个四面体，并没有处理过锯齿，只是简单的创建了四个三角形（Triangle），这并不难操作，利用以前的框架，再添加上以下代码就可以了~

注意，之前提过的，如果你的屏幕距离四面体过近的话会导致部分会被屏幕裁剪

（If you were to move it only 6 units into the screen, the cube would appear much larger than the pyramid, and parts of it might get cut off by the sides of the screen. You can play around with this setting, and see how moving the triangles further into the screen makes it appear smaller, and moving it closer makes it appear larger. The reason this happens is perspective. Objects in the distance should appear smaller :) ）

// this is my first tetrahedron

glLoadIdentity();

glTranslatef( 0.0f, 0.0f, -8.0f );

glRotatef( angle = angle >= 360 ? 2 : angle + 2, 1.0f, 1.0f, 0.0f ); glBegin(GL_TRIANGLES);

{

glColor3f( 1.0f, 0.0f, 0.0f );

glVertex3f( 0.0f, 1.0f, 0.0f );

glVertex3f( 0.0f, -1.0f, 1.0f );

glVertex3f( 1.0f, 0.0f, 0.0f );

glColor3f( 0.0f, 1.0f, 0.0f );

glVertex3f( 0.0f, 1.0f, 0.0f );

glVertex3f( 0.0f, -1.0f, 1.0f );

glVertex3f( -1.0f, 0.0f, 0.0f );

glColor3f( 0.0f, 0.0f, 1.0f );

glVertex3f( 0.0f, 1.0f, 0.0f );

glVertex3f( -1.0f, 0.0f, 0.0f );

glVertex3f( 1.0f, 0.0f, 0.0f );

glColor3f( 1.0f, 1.0f, 1.0f );

glVertex3f( 0.0f, -1.0f, 1.0f );

glVertex3f( -1.0f, 0.0f, 0.0f );

glVertex3f( 1.0f, 0.0f, 0.0f );

}

glEnd();

关于立方体的话于此是同理的，我们可以画上六个四边形，就可以了:）

2. glGenTextures(GLsizei, GLuint *) : glGenTextures tells OpenGL we want to generate one texture name (increase the number if you load more than one texture).

3. glBindTexture(GLenum, GLuint) : glBindTexture tells OpenGL to bind the named texture to a texture target. 2D textures have both height (on the Y axes) and width (on the X axes). The main function of glBindTexture is to assign a texture name to texture data.

4. glTexImage2D(GLenum target, GLint level, GLint components, GLsizei width, GLsizei height, GLint border, GLenum format, GLenum type, const GLvoid *pixels)

target

Specifies the target texture. Must be GL_TEXTURE_2D.

level

Specifies the level-of-detail number. Level 0 is the base image level. Level n is the nth mipmap reduction image.

components

Specifies the number of color components in the texture. Must be 1, 2, 3, or 4.

width

Specifies the width of the texture image. Must be 2^n + 2 * (border) for some integer n.

height

Specifies the height of the texture image. Must be 2^m + 2 * (border) for some integer m.

border

Specifies the width of the border. Must be either 0 or 1.

format

Specifies the format of the pixel data. The following symbolic values are accepted: GL_COLOR_INDEX, GL_RED,GL_GREEN, GL_BLUE, GL_ALPHA, GL_RGB, GL_RGBA, GL_LUMINANCE, and GL_LUMINANCE_ALPHA.

type

Specifies the data type of the pixel data. The following symbolic values are accepted: GL_UNSIGNED_BYTE,GL_BYTE, GL_BITMAP, GL_UNSIGNED_SHORT, GL_SHORT, GL_UNSIGNED_INT, GL_INT, andGL_FLOAT.

pixels

Specifies a pointer to the image data in memory.

5. glTexParameteri(GLenum target, GLenum pname, GLfloat param) ：

target

Specifies the target texture, which must be either GL_TEXTURE_1D, or GL_TEXTURE_2D.

pname

Specifies the symbolic name of a single-valued texture parameter. pname can be one of the following:GL_TEXTURE_MIN_FILTER, GL_TEXTURE_MAG_FILTER, GL_TEXTURE_WRAP_S, orGL_TEXTURE_WRAP_T.

param

Specifies the value of pname. GL_LINEAR ,GL_NEAREST :

Using GL_LINEAR requires alot of work from the processor/video card, so if your system is slow, you might want to use GL_NEAREST. A texture that's filtered with GL_NEAREST will appear blocky when it's stretched. You can also try a combination of both. Make it filter things up close, but not things in the distance.