OpenGL

Question

我正在编写一个概念验证程序以更加熟悉纹理，但它的行为很奇怪，因为它适用于 1x1 纹理但对所有其他纹理都无效。我多次扫描程序并查看了每个函数的参数，但无法理解为什么它对 1x1 纹理（或较大纹理中的第一个像素）工作正常，但在其他情况下显示白色方块。

这是同一个程序的图片运行 glTexImage2D 的宽度和高度参数分别为 (1, 1) 和 (2,2)。

这是显示白色方块的代码（而预期绘制 2x2 红色、绿色、蓝色、黄色行主要纹理）。

note: in(Comment, Arg) macro is equivelent to Arg, it's only used in this particular program because it's tricky to remember arguments of glTexImage2D off the top of your head.

#include <GL/glut.h>

// | reminder decorator macro.
#define in(Comment, Arg) Arg

GLubyte bm[16] = {
    0xff, 0x00, 0x00, 0xff,
    0x00, 0xff, 0x00, 0xff,
    0x00, 0x00, 0xff, 0xff,
    0xff, 0xff, 0x00, 0xff
};

GLuint tex;

void display()
{
    glClear(GL_COLOR_BUFFER_BIT);           

    glBindTexture(GL_TEXTURE_2D, tex);

    glLoadIdentity();

    // | make the square smaller to contrast our target from the background.
    glScalef(.5f, .5f, 1.f);

    glBegin(GL_TRIANGLE_FAN);
        glTexCoord2f(0.f, 0.f);
        glVertex2f(-1.f, 1.f);
        glTexCoord2f(0.f, 1.f);
        glVertex2f(1.f, 1.f);
        glTexCoord2f(1.f, 1.f);
        glVertex2f(1.f, -1.f);
        glTexCoord2f(1.f, 0.f);
        glVertex2f(-1.f, -1.f);
    glEnd();

    glFlush();
}

int main(int argc, char **argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE);
    glutCreateWindow("");

    glEnable(GL_TEXTURE_2D);        
    glGenTextures(1, &tex);
    glBindTexture(GL_TEXTURE_2D, tex);
    glTexImage2D (
        in(target, GL_TEXTURE_2D), 
        in(level, 0), 
        in(internalFormat, GL_RGBA), 
        in(width, 2), 
        in(height, 2), 
        in(border, 0), 
        in(format, GL_RGBA), 
        in(type, GL_UNSIGNED_BYTE), 
        in(data, bm)
    );
    glTexParameteri(tex, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(tex, GL_TEXTURE_MAG_FILTER, GL_NEAREST);

    glutDisplayFunc(display);
    glutMainLoop();

    return 0;
}

如果我将 in(width, 2) 更改为 in(width, 1) 并将 in(height, 2) 更改为 in(height, 1)，它会显示一个红色方块，并更改 bm 的前三个值数组，它按预期将此颜色映射到立方体。

#include <GL/glut.h>

// | reminder decorator macro.
#define in(Comment, Arg) Arg

GLubyte bm[16] = {
    0xff, 0x00, 0x00, 0xff,
    0x00, 0xff, 0x00, 0xff,
    0x00, 0x00, 0xff, 0xff,
    0xff, 0xff, 0x00, 0xff
};

GLuint tex;

void display()
{
    glClear(GL_COLOR_BUFFER_BIT);           

    glBindTexture(GL_TEXTURE_2D, tex);

    glLoadIdentity();

    // | make the square smaller to contrast our target from the background.
    glScalef(.5f, .5f, 1.f);

    glBegin(GL_TRIANGLE_FAN);
        glTexCoord2f(0.f, 0.f);
        glVertex2f(-1.f, 1.f);
        glTexCoord2f(0.f, 1.f);
        glVertex2f(1.f, 1.f);
        glTexCoord2f(1.f, 1.f);
        glVertex2f(1.f, -1.f);
        glTexCoord2f(1.f, 0.f);
        glVertex2f(-1.f, -1.f);
    glEnd();

    glFlush();
}

int main(int argc, char **argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE);
    glutCreateWindow("");

    glEnable(GL_TEXTURE_2D);        
    glGenTextures(1, &tex);
    glBindTexture(GL_TEXTURE_2D, tex);
    glTexImage2D (
        in(target, GL_TEXTURE_2D), 
        in(level, 0), 
        in(internalFormat, GL_RGBA), 
        in(width, 1), 
        in(height, 1), 
        in(border, 0), 
        in(format, GL_RGBA), 
        in(type, GL_UNSIGNED_BYTE), 
        in(data, bm)
    );
    glTexParameteri(tex, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(tex, GL_TEXTURE_MAG_FILTER, GL_NEAREST);

    glutDisplayFunc(display);
    glutMainLoop();

    return 0;
}

有人可以解释发生了什么以及我该如何解决这个问题吗？

Solution: passed tex to glTexParameteri instead of GL_TEXTURE_2D(side note: and a typo 1.1 to 1.f in glVertex2f)

#include <GL/glut.h>

// | reminder decorator macro.
#define in(Comment, Arg) Arg

GLubyte bm[16] = {
    0xff, 0x00, 0x00, 0xff,
    0x00, 0xff, 0x00, 0xff,
    0x00, 0x00, 0xff, 0xff,
    0xff, 0xff, 0x00, 0xff
};

GLuint tex;

void display()
{
    glClear(GL_COLOR_BUFFER_BIT);           

    glBindTexture(GL_TEXTURE_2D, tex);

    glLoadIdentity();

    // | make the square smaller to contrast our target from the background.
    glScalef(.5f, .5f, 1.f);

    glBegin(GL_TRIANGLE_FAN);
        glTexCoord2f(0.f, 0.f);
        glVertex2f(-1.f, 1.f);
        glTexCoord2f(1.f, 0.f);
        glVertex2f(1.f, 1.f);
        glTexCoord2f(1.f, 1.f);
        glVertex2f(1.f, -1.f);
        glTexCoord2f(0.f, 1.f);
        glVertex2f(-1.f, -1.f);
    glEnd();

    glFlush();
}

int main(int argc, char **argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE);
    glutCreateWindow("");

    glEnable(GL_TEXTURE_2D);        
    glGenTextures(1, &tex);
    glBindTexture(GL_TEXTURE_2D, tex);
    glTexImage2D (
        in(target, GL_TEXTURE_2D), 
        in(level, 0), 
        in(internalFormat, GL_RGBA), 
        in(width, 2), 
        in(height, 2), 
        in(border, 0), 
        in(format, GL_RGBA), 
        in(type, GL_UNSIGNED_BYTE), 
        in(data, bm)
    );
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);

    glutDisplayFunc(display);
    glutMainLoop();

    return 0;
}

Answer 1

当您指定 2x2 纹理时，您的纹理不是 mipmap 完整的，而是使用了 mip-mapping 缩小过滤器。根据规范，您得到的结果是正确的结果。

您的错误在于您试图设置非 mipmapping GL_NEAREST 过滤器：

glTexParameteri(tex, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

glTexParameter 需要纹理绑定点，即 GL_TEXTURE_2D，而不是纹理名称。因此，此调用将产生 GL_INVALID_ENUM 错误并且没有其他影响。

OpenGL - 如何让这个程序适用于大于 1x1 的纹理？

OpenGL - How can I make this program work for textures larger than 1x1?

c

textures

texture-mapping

texture2d