Question

我有两个纹理和一个三角形图元（其顶点的颜色由glColor4f定义）。

纹理A看起来像这样：

纹理B看起来像这样：

三角形基元P看起来像这样：

当我渲染纹理A，然后渲染纹理B时，我得到了预期的结果，即矩形的中间是透明的。

但是，如果我渲染图元P，然后渲染纹理A，然后渲染纹理B，则会得到错误的颜色。 P不是纯红色，纹理颜色全部变为黑色。

如何解决此问题，以便保持适当的透明度和颜色。

纹理参数：

    GL_CALL(glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR));
    GL_CALL(glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR));
    GL_CALL(glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_BORDER));
    GL_CALL(glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_BORDER));
    GLfloat debugColor[] = {1.0f, 0.0f, 1.0f, 1.0f};
    GL_CALL(glTexParameterfv(GL_TEXTURE_2D, GL_TEXTURE_BORDER_COLOR, debugColor));

混合功能：

GL_CALL(glEnable(GL_BLEND));
GL_CALL(glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA));

P，A和B的渲染：

        if(true)
        {
            // Render Primitive P

            GL_CALL(glBegin(GL_TRIANGLES));

            GL_CALL(glColor4f(1.0f, 0.0f, 0.0f, 1.0f));
            GL_CALL(glVertex2f(-0.5f, -0.5f));

            GL_CALL(glColor4f(1.0f, 0.0f, 0.0f, 1.0f));
            GL_CALL(glVertex2f(0.0f, 0.5f));

            GL_CALL(glColor4f(1.0f, 0.0f, 0.0f, 1.0f));
            GL_CALL(glVertex2f(0.5f, -0.5f));

            glEnd();
        }
        if(true)
        {
            // Render Texture A

            GL_CALL(glBindTexture(GL_TEXTURE_2D, textureId));
            GL_CALL(glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, imageWidth, imageHeight, 0,
                                 GL_RGBA, GL_UNSIGNED_BYTE, image));

            real32 screenPercentage = 0.25f;

            GL_CALL(glBegin(GL_TRIANGLES));

            // Lower triangle
            GL_CALL(glTexCoord2f(0.0f, 0.0f));
            GL_CALL(glVertex2f(-screenPercentage, screenPercentage));

            GL_CALL(glTexCoord2f(1.0f, 0.0f));
            GL_CALL(glVertex2f(screenPercentage, screenPercentage));

            GL_CALL(glTexCoord2f(1.0f, 1.0f));
            GL_CALL(glVertex2f(screenPercentage, -screenPercentage));

            //  Upper triangle
            GL_CALL(glTexCoord2f(0.0f, 0.0f));
            GL_CALL(glVertex2f(-screenPercentage, screenPercentage));

            GL_CALL(glTexCoord2f(1.0f, 1.0f));
            GL_CALL(glVertex2f(screenPercentage, -screenPercentage));

            GL_CALL(glTexCoord2f(0.0f, 1.0f));
            GL_CALL(glVertex2f(-screenPercentage, -screenPercentage));

            glEnd();
        }

        if(true)
        {
            // Render Texture B

            GL_CALL(glBindTexture(GL_TEXTURE_2D, textureId));
            GL_CALL(glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, window[0].offscreenBuffer.width, window[0].offscreenBuffer.height, 0,
                                 GL_RGBA, GL_UNSIGNED_BYTE, window[0].offscreenBuffer.data));

            real32 screenPercentage = 1.0f;

            GL_CALL(glBegin(GL_TRIANGLES));

            // Lower triangle
            GL_CALL(glTexCoord2f(0.0f, 0.0f));
            GL_CALL(glVertex2f(-screenPercentage, screenPercentage));

            GL_CALL(glTexCoord2f(1.0f, 0.0f));
            GL_CALL(glVertex2f(screenPercentage, screenPercentage));

            GL_CALL(glTexCoord2f(1.0f, 1.0f));
            GL_CALL(glVertex2f(screenPercentage, -screenPercentage));

            // Upper triangle
            GL_CALL(glTexCoord2f(0.0f, 0.0f));
            GL_CALL(glVertex2f(-screenPercentage, screenPercentage));

            GL_CALL(glTexCoord2f(1.0f, 1.0f));
            GL_CALL(glVertex2f(screenPercentage, -screenPercentage));

            GL_CALL(glTexCoord2f(0.0f, 1.0f));
            GL_CALL(glVertex2f(-screenPercentage, -screenPercentage));

            glEnd();
        }

编辑：尝试@ Rabbid76的解决方案后：

        glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        if(true)
        {
        // Render triangle with all vertices having color 1.0f, 0.0f, 0.0f, 1.0f 
        }
        if(true)
        {
        // Render texture A with color set to 1.0f, 1.0f, 1.0f, 1.0f and the appropriate texture u,v coordinates
        }

        if(true)
        {
            // Render texture B with color set to 1.0f, 1.0f, 1.0f, 1.0f and the appropriate texture u,v coordinates
        }

我得到以下结果：

即使所有三个实体的alpha为1.0f，空心区域的alpha为0.0f，颜色仍然不正确

Answer 1

如果启用纹理，则默认情况下，纹理像素的颜色将乘以当前颜色，因为默认情况下纹理环境模式（if (preg_match('/^([1-9]|[1-2][0-9]|[3][0-1])\-([1-9]|[1][0-2])\-(?:20)([1][8-9]|[2-9][0-9])$/', $date)) { // Do stuff }）为GL_TEXTURE_ENV_MODE。参见glTexEnv。

这将导致纹理的纹理像素的颜色与glColor4f设置的最后一个颜色“混合”。
渲染纹理时，仍会设置三角形的红色，这将导致纹理着色为红色。绿色和蓝色通道完全消失了，并且由于纹理没有红色通道，因此剩下的都是黑色。

要解决您的问题，必须在渲染纹理之前设置白色：

GL_MODULATE

并在渲染三角形之前禁用glColor4f(1.0f, 1.0f, 1.0f, 1.0f);，但在渲染纹理之前将其启用。
请注意，始终存在纹理绑定，没有“没有纹理”之类的东西，默认纹理对象0也是有效对象。这将导致纹理查找呈现完全黑色，并与由GL_TEXTURE_2D设置的红色混合：

glColor4f

Alpha混合纹理和图元

1 个答案: