Question

我需要显示一些索引图形文件，另外还有每像素alpha通道。此外，我需要确保我可以随时更改调色板，结果图像也会改变。为此，我首先使用了软件像素预计算，但这对于实时渲染来说太慢了，所以我决定编写一个将在GPU端处理索引纹理的着色器。问题是第二个纹理（rec_colors）没有加载（至少看起来是这样 - 从该采样器读取的每个纹素都显示为空）。

来自零纹理的数据正确读取，导致右图像的黑色图像：）

与着色器初始化相关的代码：

Application::Display->GetRC();
glewInit();
if(!GLEW_VERSION_2_0) return false;

char* code_frag = loadCode("shader.frag");
char* code_verx = loadCode("shader.verx");

aShader_palette = glCreateShader(GL_FRAGMENT_SHADER);
//glShaderSource(aShader_palette, 1, &aShaderProgram_palette, NULL);
glShaderSource(aShader_palette, 1, (const GLchar**)&code_frag, NULL);
glCompileShader(aShader_palette);

GLint compiled = 0;
glGetShaderiv(aShader_palette, GL_COMPILE_STATUS, &compiled);

if(!compiled)
{
    /* error-handling */
}

GLuint texloc = glGetUniformLocation(aShader_palette, "rec");
glUniform1i(texloc, 0);
texloc = glGetUniformLocation(aShader_palette, "rec_colors");
glUniform1i(texloc, 1);

glsl_palette_Program = glCreateProgram();
glAttachShader(glsl_palette_Program, aShader_palette);
glLinkProgram(glsl_palette_Program);

与渲染相关：

glPushAttrib(GL_CURRENT_BIT);
glColor4ub(255, 255, 255, t_a); // t_a is overall alpha of sprite displayed
glUseProgram(glsl_palette_Program); // this one is a compiled/linked shader declared above
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_RECTANGLE_ARB, this->m_SpriteData[idx].texture);
glActiveTexture(GL_TEXTURE1); // at this point, it looks like texture unit is actually changed (I checked that via glGetIntegerv)
glBindTexture(GL_TEXTURE_RECTANGLE_ARB, this->m_PaletteTex);
glTexSubImage2D(GL_TEXTURE_RECTANGLE_ARB, 0, 0, 0, 256, 1, GL_RGBA, GL_UNSIGNED_BYTE, palette); // update possibly changed palette on each render
glActiveTexture(GL_TEXTURE0);
glBegin(GL_QUADS);
    glTexCoord2i(0, 0);
    glVertex2i(x, y);
    glTexCoord2i(0, this->GetHeight(idx));
    glVertex2i(x, y+this->GetHeight(idx));
    glTexCoord2i(this->GetWidth(idx), this->GetHeight(idx));
    glVertex2i(x+this->GetWidth(idx), y+this->GetHeight(idx));
    glTexCoord2i(this->GetWidth(idx), 0);
    glVertex2i(x+this->GetWidth(idx), y);
glEnd();
glActiveTexture(GL_TEXTURE1);
glUnbindTexture(GL_TEXTURE_RECTANGLE_ARB); // custom macro
glActiveTexture(GL_TEXTURE0);
glUnbindTexture(GL_TEXTURE_RECTANGLE_ARB);
glUseProgram(0);
glPopAttrib();

着色器代码：

#extension GL_ARB_texture_rectangle : enable

uniform sampler2DRect rec;
uniform sampler2DRect rec_colors;

void main(void)
{
    vec4 oldcol = texture2DRect(rec, gl_TexCoord[0].st);
    vec4 newcol = texture2DRect(rec_colors, vec2(oldcol.r*255.0, 0.0)); // palette index should be*255 bcs rectangle coordinates aren't normalized
    gl_FragColor.rgb = newcol.rgb;
    gl_FragColor.a = oldcol.g; // alpha from green part
}

Google搜索了很多，我发现的任何类似帖子都是通过修复glUniform1i调用中的纹理单元ID来解决的，但对我来说看起来绝对正常（至少TEXTURE0正确加载到rec中）。

Answer 1

您是否在glGetError的任何地方检查错误？我相信你做错了什么。 glGetUniformLocation应该针对链接的程序而不是着色器执行。在程序关联之前，您正在调用glGetUniformLocation。

请参阅手册页中的相关文字：http://www.opengl.org/wiki/GLAPI/glGetUniformLocation

The actual locations assigned to uniform variables are not known until the program object is linked successfully. After linking has occurred, the command glGetUniformLocation can be used to obtain the location of a uniform variable. Uniform variable locations and values can only be queried after a link if the link was successful.

在开发过程中，您应始终每帧检查一次glGetError的opengl错误。在您上网寻求帮助之前，它会提醒您这些问题。

具有片段着色器的多个纹理单元不起作用

1 个答案: