Support for texture layers.

src/AbstractTexture.cpp

@@ -17,6 +17,19 @@
 
 namespace Magnum {
 
+#ifndef DOXYGEN_GENERATING_OUTPUT
+/* Check corretness of GL_TEXTURE0 + N == GL_TEXTUREN */
+#define texture_assert(num) static_assert(GL_TEXTURE0 + num == GL_TEXTURE##num,\
+    "Unsupported constants for GL texture layers")
+texture_assert(0); texture_assert(8);  texture_assert(16); texture_assert(24);
+texture_assert(1); texture_assert(9);  texture_assert(17); texture_assert(25);
+texture_assert(2); texture_assert(10); texture_assert(18); texture_assert(26);
+texture_assert(3); texture_assert(11); texture_assert(19); texture_assert(27);
+texture_assert(4); texture_assert(12); texture_assert(20); texture_assert(28);
+texture_assert(5); texture_assert(13); texture_assert(21); texture_assert(29);
+texture_assert(6); texture_assert(14); texture_assert(22); texture_assert(30);
+texture_assert(7); texture_assert(15); texture_assert(23); texture_assert(31);
+
 /* Check correctness of binary OR in setMinificationFilter(). If nobody fucks
    anything up, this assert should produce the same results on all dimensions,
    thus testing only on AbstractTexture. */
@@ -27,6 +40,7 @@ static_assert(((AbstractTexture::NearestNeighborFilter|AbstractTexture::BaseMipL
               ((AbstractTexture::LinearFilter|AbstractTexture::NearestMipLevel) == GL_LINEAR_MIPMAP_NEAREST) &&
               ((AbstractTexture::LinearFilter|AbstractTexture::LinearMipInterpolation) == GL_LINEAR_MIPMAP_LINEAR),
     "Unsupported constants for GL texture filtering");
+#endif
 
 void AbstractTexture::setMinificationFilter(Filter filter, Mipmap mipmap) {
     /* Only base mip level is supported on rectangle textures */

src/AbstractTexture.h

@@ -108,11 +108,13 @@ class AbstractTexture {
 
         /**
          * @brief Constructor
+         * @param layer     Texture layer (number between 0 and 31)
          * @param target    Target, e.g. @c GL_TEXTURE_2D.
          *
          * Creates one OpenGL texture.
          */
-        inline AbstractTexture(GLenum target): target(target) {
+        inline AbstractTexture(GLint layer, GLenum target): target(target), _layer(layer) {
+            glActiveTexture(GL_TEXTURE0 + layer);
             glGenTextures(1, &texture);
         }
 
@@ -127,6 +129,7 @@ class AbstractTexture {
 
         /** @brief Bind texture for usage / rendering */
         inline void bind() const {
+            glActiveTexture(GL_TEXTURE0 + _layer);
             glBindTexture(target, texture);
         }
 
@@ -137,6 +140,7 @@ class AbstractTexture {
          * particular one.
          */
         inline void unbind() const {
+            glActiveTexture(GL_TEXTURE0 + _layer);
             glBindTexture(target, 0);
         }
 
@@ -231,6 +235,7 @@ class AbstractTexture {
         };
 
     private:
+        const GLint _layer;
         GLuint texture;
 };
 

src/CubeMapTexture.h

@@ -48,10 +48,11 @@ class CubeMapTexture: public Texture2D {
     public:
         /**
          * @brief Constructor
+         * @param layer     Texture layer (number between 0 and 31)
          *
          * Creates texture with target @c GL_TEXTURE_CUBE_MAP.
          */
-        inline CubeMapTexture(): Texture2D(GL_TEXTURE_CUBE_MAP) {}
+        inline CubeMapTexture(GLint layer = 0): Texture2D(layer, GL_TEXTURE_CUBE_MAP) {}
 
     protected:
         /** @brief Deleted. Use setDataPositiveX() and others instead. */

src/Texture.h

@@ -53,13 +53,14 @@ template<size_t dimensions> class Texture: public AbstractTexture {
 
         /**
          * @brief Constructor
+         * @param layer     Texture layer (number between 0 and 31)
          * @param target    Target, e.g. @c GL_TEXTURE_RECTANGLE. If not set,
          *      target is based on dimension count (@c GL_TEXTURE_1D,
          *      @c GL_TEXTURE_2D, @c GL_TEXTURE_3D).
          *
          * Creates one OpenGL texture.
          */
-        inline Texture(GLenum target = DataHelper<dimensions>::target()): AbstractTexture(target) {}
+        inline Texture(GLint layer = 0, GLenum target = DataHelper<dimensions>::target()): AbstractTexture(layer, target) {}
 
         /**
          * @brief Set wrapping